The Portuguese Under 21 international was handed a 15 minute spell at the end of the clash at Glanford Park but showed enough in that short space of time to impress team-mate Smalling.
Bebe has impressed fellow United players with his raw speed in training showed glimpses of his electric pace during Wednesday night's third round tie.
Debut boy: Bebe impressed team-mates on his first outing for United
'Since he's come in, he's become sharper every day,' said the Smalling. 'He's really improving and working on his fitness. Tonight he really caused their full-back problems, coming in from the wing'
'Hopefully we'll see him produce that kind of form in many games to come.'
Assistant manager Mike Phelan took charge of the team in Sir Alex Ferguson's absence as United cruised to a 5-2 victory, and was more than happy with what he saw from the Reds' newest recruit.
'The scoreline gave us the opportunity to give Bebe a little look at what Manchester United's all about. I thought he responded very well,' Phelan told MUTV.
'There were fleeting moments of pace and power, and he got a little bit excited now and again. But it's important that players like him get these opportunities.'
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