David McGoldrick's first two Premier League goals proved pivotal as Sheffield United cruised to a 3-0 win against third-placed Chelsea to blow open the Premier League top four race.
Sheffield broke the deadlock against Chelsea after 18 minutes as Oliver McBurnie's deflected effort prompted a brilliant reflex save from Kepa Arrizabalaga. However, the ball fell perfectly to McGoldrick in the six-yard box, who made no mistake to finally end his goal drought in England's top-flight.
Chelsea were 0-2 down after the half-hour mark after Ben Osborn and Enda Stevens combined devastatingly down the left-hand side. Stevens' cross was met by McBurnie, who took advantage of poor Chelsea defending to head home, in the process scoring his sixth league goal of the campaign.
Chelsea failed to take advantage of their sustained periods of possession and despite a few encouraging flashes, found themselves with a mountain to climb and a two-goal deficit in tow.
Frank Lampard made a few tactical alterations and substitutions to begin the second-half, though it was more of the same as Chelsea continued to lack urgency in their attacking endeavours.
Olivier Giroud and Tammy Abraham came close with chances, but neither was able to reduce the arrears before Sheffield scored a killer third before full-time to end the game as a contest.
Chris Wilder's Sheffield were clever in possession, held the ball up well and crucially took their chances. McGoldrick probably couldn't believe his luck after being gifted a second after 77 minutes when Lys Mousset's cross was poorly defended by Chelsea substitute Antonio Rudiger.
On hand to apply the finishing touch, the 32-year-old wheeled away to celebrate sinking a Chelsea side whose top-four credentials have weakened significantly with this result.
It could have been a heavier defeat for Chelsea, but for Mousset and Stevens firing wide from promising chances late on. Without further ado, here's a look at five talking points as Sheffield United were impressive enroute to inflicting Chelsea's second defeat in their last four matches.
Five talking points in Chelsea's 0-3 loss to Sheffield United
#1: Reece James has to start more often
Ignore the reactionary comments from rival supporters and angry fans on social media. Avoid comparisons with youngsters in the same position - Trent Alexander-Arnold (21) and Aaron Wan-Bissaka (22) - and just watch a game for yourself.
It's easy to see why Reece James is so highly rated by Chelsea. But displays like the one he put up against Sheffield tonight reiterate why he needs to play more regularly, both for his development and invaluable experience. This was a forgettable away performance from Chelsea, yet the 20-year-old was among the visitor's best players before being replaced in an attacking change for Callum Hudson-Odoi with 15 minutes left.
The quality of James' crossing has both been marvelled and used as a stick to criticise him with, as it's easy to highlight inconsistent deliveries when you're trailing in games and need a way back into proceedings. He connected with three of seven attempts, won four of ten duels and lost possession 15 times - so why does he deserve a starting berth on that side of the pitch?
It's easy to forget that he's still 20, and this is his first Premier League campaign and one where he hasn't had adequate support from teammates. Willian's defensive involvement in McBurnie's goal, or lack thereof, rather amplifies my point here.
Compared with the competition, James is aggressive but channels that energy the right way in one-on-one challenges. He was reliable with his passing (86.1% accuracy, game-high three key passes) and forced Dean Henderson into a sharp save from distance before half-time.
He made a necessary defensive recovery early in the second-half as his Chelsea teammates were again caught high up the pitch and importantly refused to stop trying to help create chances.
#2: McGoldrick's frustrating goal drought finally ends
After 26 appearances, David McGoldrick has finally broken his Premier League scoring duck.
He has threatened on multiple occasions, had goals disallowed by VAR and has missed golden opportunities, but the Ireland international was a grateful benefactor as Chelsea's defence gifted him two close-range chances that he wasn't going to pass up.
His hard work and endeavour have presented him with 15 big chances that he has squandered to date this term, a statistic he'll hope doesn't increase in the final few weeks.
But it's that tireless nature, impressive attack positioning and ability to hold up play confidently under pressure that has seen McGoldrick continue to assert himself as a mainstay in Chris Wilder's overachieving side, despite previously being scoreless in England's top-flight.
His first strike was an example of his great anticipation in the six-yard box after McBurnie's initial effort was parried by the alert Chelsea goalkeeper who could, however, do nothing to stop the rebound.
As for McGoldrick's second, Chelsea again hand-wrapped a present that he gratefully buried from close-range. Rudiger's attempted clearance resembled an under-hit pass rather than a boot to safety, and McGoldrick slipped through unchallenged to slam home Sheffield United's third goal.
Importantly, his on-ball movement was critical during the build-up to Sheffield United's third goal: carrying possession forward in transition, teeing up Mousset to his right and ghosting into the box to finish a poorly defended counter-attack.
He should have had an assist too, again releasing Mousset - this time after outmuscling Jorginho with worrying ease - who chipped his effort narrowly wide of Kepa Arrizabalaga's far post.
It's a welcome morale boost at precisely the right time for McGoldrick, who'll be hopeful of maintaining this level of performance in the final third heading into the new campaign.
#3: Chelsea's defensive frailties exposed again
Chelsea conceded three against West Ham on July 1, almost dropped two points after conceding twice to Crystal Palace six days later and have again conceded thrice against Sheffield United.
An unsettling pattern is emerging for Frank Lampard's Chelsea, and it's not one that has been a secret throughout an inconsistent campaign to date. Andreas Christensen and Kurt Zouma were caught ball-watching and duly punished for dithering out of possession.
The inability to sense danger on two separate occasions in the first-half was worrying, as both were slow to react and were caught out of position for Sheffield' first two goals.
It just reinforced the point that Rudiger - scapegoated for his display in Chelsea's defeat to West Ham - isn't the Blues' only centre-back conundrum.
Fikayo Tomori (muscle injury) remains sidelined and while speculation suggests he could be loaned out in a deal that brings highly-rated Declan Rice back to the club, the Blues cannot pin their hopes on another young Englishman to save their defensive woes. It goes much deeper than that.
Jorginho failed to provide ample protection for his backline and drifted through the game for sustained periods despite his orchestrative abilities from deep. Questions remain over Christensen's suitability at the heart of Lampard's Chelsea defence and Zouma - their midweek saviour at Crystal Palace - didn't exactly cover himself in glory against Sheffield United.
#4: Lampard's tactical alterations fail to inspire Chelsea comeback
Frank Lampard knew he needed to change things after a frustrating half saw Chelsea with a significant deficit to overturn. His team had passed their opponents to death at times, yet were losing duels and struggled in attempts to breakdown a disciplined Blades backline.
Mason Mount struggled to dovetail with Christian Pulisic down the left and was subsequently sacrificed, while Christensen - who twisted his ankle minutes earlier - was also replaced.
On came Marcos Alonso, notorious for his attacking capabilities and baffling defensive positioning, as well as Rudiger. It was an admission that Chelsea needed to match, then eventually better, their opponents.
Changing shape to a 3-4-3 gave Alonso and James a licence to play as wingbacks, while Azpilicueta shifted into a central defensive trio alongside Rudiger and Zouma. It didn't have the desired effect for Chelsea, though.
Pulisic was tightly man-marked and struggled to make an impact the game. Ross Barkley was quietly one of Chelsea's better players, yet was left frustrated by a sloppy Abraham upfront. Willian had his moments, but Sheffield United had a cushion to protect and were more than happy to defend in numbers whenever Chelsea edged closer towards Henderson's area.
John Egan (nine clearances, three interceptions, one tackle) and Jack O'Connell (five clearances, three interceptions, one block) were particularly strong under pressure despite some rather nervy distribution. On came Phil Jagielka too, whose excellently-timed sliding block to deny Abraham's goal-bound effort rather typified a frustrating afternoon for Chelsea.
#5: Champions League race intensifies with three matches left to play
After their last-gasp 1-0 win over Wolves in midweek, Sheffield United have now leapfrogged Nuno Espirito Santo's men into sixth place. Wolves host Everton on Sunday lunchtime, though the race for Champions League places has been blown wide open with third-placed Chelsea's loss to Sheffield United.
Chelsea, who could have opened up a four-point gap to fourth-placed Leicester City by beating Sheffield United, may instead find themselves outside the top-four altogether by Monday night.
Manchester United, unbeaten since January, host mid-table Southampton, while Leicester City face a trip to the south coast against relegation-threatened Bournemouth.
With three league fixtures left to play, Chelsea's defensive woes and creative inconsistencies have left the side in a precarious situation.
Only two points separate third from fifth at the time of writing, though it'll be interesting to see what twists and turns are next in a compelling race for Champions League football.
Stats' source: SofaScore.