Liverpool handed Manchester United one of their worst-ever Premier League defeats as they beat Ole Gunnar Solksjaer's side 5-0 at Old Trafford. Naby Keita and Diogo Jota gave the Reds an early advantage before Mohamed Salah took centrestage with a sumptuous hat-trick.The visitors were on the front foot right from the get-go. Keita opened the scoring in the fifth minute to give the Reds a well-deserved lead. Klopp's side then sunk the Red Devils with three more unanswered first-half goals.Salah soon added another after the break to become the first-ever visiting player to score a hat-trick at Old Trafford in Premier League history. After that, it was just game management from Klopp's side as they passed the ball effortlessly against a lacklustre Manchester United side.Liverpool FC@LFC𝗪𝗛𝗔𝗧. 𝗔. 𝗣𝗘𝗥𝗙𝗢𝗥𝗠𝗔𝗡𝗖𝗘. ✊🔴#MUNLIV10:53 AM · Oct 24, 20217423323893𝗪𝗛𝗔𝗧. 𝗔. 𝗣𝗘𝗥𝗙𝗢𝗥𝗠𝗔𝗡𝗖𝗘. ✊🔴#MUNLIV https://t.co/Lv0MtFIp9MOn that note, here's a look at the five biggest talking points from the game:#5 How bad can it get for Manchester United?Manchester United vs Liverpool - Premier LeagueIt is fair to say that it has never been worse than this for Manchester United. The Red Devils were 4-0 down in the first half for the first time in Premier League history, and they looked absolutely clueless throughout the game.OptaJoe@OptaJoe4 - Manchester United are four goals behind at the half-time interval in the @premierleague for the very first time. Smashed.9:52 AM · Oct 24, 202122626414 - Manchester United are four goals behind at the half-time interval in the @premierleague for the very first time. Smashed. https://t.co/SdunQYeSKUUnited's press was disorganised, and they weren't able to attack efficiently with the very little possession they managed. Solksjaer's side are now on one of their worst-ever defensive runs, managing just one clean sheet in their last 21 games across competitions. United have not kept a clean sheet in 12 home games now across competitions.This wasn’t just about a horrible no-show from Solskjaer's side; this was about their arch-rivals coming to Old Trafford and making it look like child's play.#4 Liverpool's Naby Keita suffers yet another injury setbackNaby Keita got injured against Manchester United.Naby Keita truly showcased his all-round abilities in this game to the fullest. He started brightly as the most advanced member of Liverpool's midfield three. The midfielder made no mistake in finishing off Mohamed Salah's sublime pass just five minutes into the game. That marked Liverpool's quickest-ever goal at Old Trafford.OptaJoe@OptaJoe04:42 - Naby Keita's opening goal is the earliest Premier League goal Liverpool have ever scored at Old Trafford. Sliced.9:10 AM · Oct 24, 202191519604:42 - Naby Keita's opening goal is the earliest Premier League goal Liverpool have ever scored at Old Trafford. Sliced. https://t.co/99dWhVJR7dEight minutes later, he supplied an exquisite delivery to Trent Alexander Arnold for Liverpool's second. He then bagged an assist for Salah's first goal of the night. The 26-year old has now scored three goals this season, after going goalless for the entirety of last campaign.However, as has often been the case during his time at Liverpool, Keita suffered yet another injury setback, courtesy of a reckless Paul Pogba challenge in the second half. Jurgen Klopp will surely hope he is back soon given how pivotal he has been for the Reds this season.