United will travel to west London for their quarter-final first leg five weeks after losing 2-1 in the Barclays Premier League to their arch-rivals, with Smalling having conceded the spot-kick for what proved the Blues' winning goal.
The defender was controversially adjudged to have tripped Yury Zhirkov, one of several decisions that went against the visitors and sent manager Sir Alex Ferguson over the edge, earning him a touchline ban.
Some stand-in: Smalling has had to fill in for the often injured Rio Ferdinand and Nemanja Vidic this season
Smalling said: 'I still don't think it was a penalty and that I was hard done by. But you get those in your career and what's important is how you react.
'I've managed to be involved, play games and keep my momentum going. I don't feel I've got anything to prove.'
The Chelsea defeat sparked United's first real wobble of the season and they also went down 3-1 at Liverpool. But they won their next three matches in all competitions before producing a trademark sensational late comeback to beat West Ham on Saturday.
With Arsenal and Chelsea both drawing, the 4-2 win left United a clear run at the Premier League title, while the treble remains very much on for Ferguson's side.
Smalling, 21, has played a massive part during what is his maiden season at Old Trafford, playing 27 times as Rio Ferdinand and Nemanja Vidic have struggled with injury. He added of Wednesday's game: 'It's another massive stage for myself. To be able to play in these latter stages of the Champions League is what most players in the world would dream to be a part of.
Head to head: Manchester United and Chelsea meet in the Champions League quarter-finals this week
'Rio has guided me all the way through and it's great to see him getting back training. He's had such bad luck with injury. We're starting to get everyone back now and we need them at this important stage of the season.'
Smalling has also been indoctrinated into United's never-say-die culture, playing a part in all three of this season's comebacks from 2-0 behind - against Aston Villa, Blackpool and now the Hammers.
'Everybody just sticks together,' said the former Fulham trainee. 'It shows how big this club is and the emphasis on things, how we don't give up. I'm definitely fitting into that philosophy. I'm starting to get a feel of the club's never-say-die attitude and I don't think many others teams possess that.'
Wayne Rooney inspired the turnaround with a dramatic 14-minute hat-trick, a feat that prompted Smalling and his team-mates to sign the match ball.
'A few people were putting a few dodgy little messages on it,' Smalling said. 'I saw Michael Owen writing something about his first touch on one of the goals but it was all jokes. To be a part of a comeback like that and to sign the ball for one of the biggest players is incredible but I really feel like I'm playing my part.'
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Explore more:People: Alex Ferguson, Michael Owen, Nemanja Vidic, Wayne Rooney, Rio Ferdinand Places: Liverpool, London