The Owls skipper was down after the City clash on Saturday and was not happy with his first-half performance, but despite making personal errors, the Scotsman had a fine second period.
But now all focus has to be on the Brentford clash and Bullen believes that Wednesday will not be playing for the odd draw - they will be out to win both legs.
On the City game, he told Footymad: "We had a bit of a fightback. The conditions were very blustery and we found it difficult. We found it hard to get on top in the first half: we made mistakes, personal mistakes from me and without that we would have been looking at a win instead of a defeat.
"But let us now get that behind us," he said looking forward to the Bees clash. "The big time is coming now on Thursday and Monday and we have to go in positively for Brentford.
"If we play positively – we can do it and we have to believe we can do it. There’s no point hanging back and trying to play for a draw, we have to go for it because we have done the hard job and now it’s just a case of taking it a small step further and having a good shot at trying to get to Cardiff."
More from Lee this week and tomorrow, we speak to a young Owls star who is relishing the prospect of a play-off semi-final.
Tickets for OAC holders for the away game go on sale on Thursday at 5pm with voucher 14 from the season ticket - all other tickets go on sale to season ticket holders with the same voucher on the Friday morning.