A win for bottom club Reading or second bottom QPR would have been enough to keep alive their slim survival hopes with three games to go.
Currently, United are unbeaten since going down to Romanian side Cluj in a 'meaningless' Champions League group game at the start of December while their last league loss came at Norwich three months ago.
Benitez admits the slip-ups had been costly but insisted the dethroned European champions were getting stronger overall.
Premier League newboys Reading re-signed former England defender Nicky Shorey on a free transfer on Tuesday.
Micah Richards scored the only goal to earn Manchester City a 1-0 win over Reading in the FA Cup quarterfinals on Sunday and set up a semifinal clash with Manchester United.