After losing to Steaua Bucharest on Wednesday, Chelsea found themselves trailing 2-0 to Manchester United after just 11 minutes on Sunday. At the end of the first half, it looked like the Blues' season was all but over.
The second 45 minutes brought out a very different Chelsea side. Rafael Benitez brought on Eden Hazard and John Obi Mikel in the 52nd minute, and the game changed dramatically. The Blues dominated and were rewarded with goals from Hazard and Ramires.
Chelsea forced a quarter-final replay with United, but they will certainly be kicking themselves for not winning the match. On the other hand, Sir Alex Ferguson will be angry at his side's lethargic second-half display.
Here are four things we learned or were reinforced by Chelsea's performance at Old Trafford.