Chelsea have won only one of their last five league games and were outclassed by United, who are just one point behind them in third place with two games in hand.
Scolari admitted his side must not repeat the kind of performance they gave in the second half at Old Trafford and called for his players to get their challenge back on course.
"Don't think if we lose one game we are finished. We have 17 games left and we will fight to the last," Scolari told reporters.
"You never know what will happen but if we play like we did today for the next three of four games we will not win.
"But now is the time for me and the players to think about the future. We can lose everything or we can be men and we can improve."
Scolari said the defeat by United, watched by former Chelsea coach Jose Mourinho in the Old Trafford crowd, had done 'very big damage' to his side's confidence after they went behind to a Nemanja Vidic header and then capitulated after the break when Wayne Rooney and Dimitar Berbatov added further goals.
He added: "The performance for the first 45 minutes was very good. It was the same as Manchester United but we conceded a goal in the last minute of the first half and that changed the game.
"After the goal they played with more freedom. We tried to put more players forward and that gave them the space they wanted to play. In the second 45 minutes they played very well. They were better than us."
Veteran United forward Ryan Giggs produced a masterful performance to inflict Chelsea's first away defeat of the season and put Alex Ferguson's side within five points of leaders Liverpool with two games in hand.
"I'm not too bothered what it does to them (Chelsea) but what it does to us is gives us confidence," Giggs told Sky Sports.
"We had one point out of the previous three meetings against the top sides and we were disappointed with that.
"We have obviously got them all at home now and we have got to make the most of it like we did today."
United face Wigan on Wednesday night and then Bolton next Saturday and with maximum points would top the table before Liverpool play their next game against Everton next Monday.
"It's down to us now," Rooney told MUTV. "If we win the two games we will be top of the league, maybe even if it's just until Liverpool play Everton.
"But on Saturday night we want to look at the table and be top."
‘He instantly popped into our ratings as one of the best U21 midfielders in Europe. The impressive thing is Slot has made him into more of a no.6' Inside Ryan Gravenberch's transformation at Liverpool
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
