Indeed, Sir Alex told MUTV he thought United were "lucky" to still be in the FA Cup following Sunday's second-half performance. The boss believes last Tuesday's Champions League tie against Real Madrid took its toll on some of his players, who looked "knackered" against Chelsea.
"I think you could see it in a few of the guys' legs," Rio agreed. "As the game stretched and became more open there were a couple of tired legs out there. But that's no excuse. We should have had the game sewn up well before then.
"We're still in the FA Cup, though, and Wembley's there, waiting for either us or Chelsea to go through. Hopefully it's us.
"We're confident [we can win the replay]. We have the tools and the players to win at Stamford Bridge. We've been there this season and done very well. With the squad we've got we don't fear going anywhere."