Juan Mata admitted Sunday's 4-0 Premier League defeat versus Chelsea was a painful experience for Manchester United.
Chelsea needed only 30 seconds to open the scoring via Pedro, with Gary Cahill doubling his side's lead in the 21st minute.
United failed to get back in the game in the remaining 70 minutes and Eden Hazard and N'Golo Kante poured even more salt into the wounds of Jose Mourinho's men after the break.
"This is a painful result," former Chelsea midfielder Mata admitted to Sky Sports. "From the first minute it started very badly.
"I felt that whenever we were close to their goal, they scored, every time, and that was the key to the game.
"It is just three points, we have another important game in a few days so we need to learn from our mistakes."