#2 Holding a high line of defense
At the start of the game, Lampard knew that Manchester United's strength is their pace on the counter but that didn't stop him from playing a high line of defense. The effect that had on the game was massive as both Anthony Martial and Marcus Rashford were using their pace and trying to get in behind that Chelsea defense.
Also, playing both the full-backs nice and high in possession had an adverse effect on Chelsea's ability to stop United from counter-attacking. Solskjaer instructed both Rashford and Martial to not always track back and help the defense which meant whenever the Blues lost the ball, either Rashford or Martial had lots of open spaces to work with and United's third and fourth goal was a testament to this.
Kurt Zouma and Cesar Azpilicueta didn't have great games defensively and against big teams going forward, Lampard will want his team to look more assured at the back.