Chelsea face an uphill struggle to reach the Champions League last eight but Willian is confident they can pull off a shock win in Barcelona next month.
Willian came close to upstaging Argentina superstar Lionel Messi in Tuesday night's first leg, firing the Blues into the lead having previously twice been denied by a post.
However, Messi had the final word when he capitalised on a rare Chelsea defensive error to bag his first goal against the west Londoners at the ninth attempt and secure a 1-1 draw.
Nevertheless, Willian saw enough in Chelsea's performance at Stamford Bridge to suggest they can upset the odds in the second leg.
"In a difficult game we played very well," he told the club website. "We had to stay compact, we had a plan and we did exactly as we expected.
"They had the ball and we expected to counter-attack, and we could win this game. But we did not and the result is still open, we have to go there and try to win.
"Barcelona had more possession but they did not create more dangerous chances to score. We can go there and make the game.
"To play in the Nou Camp is totally different and we have go there with the same mentality and try to win the game.
"We were good, we played very well but we made a mistake and then we suffered a goal - but we can go to Barcelona and do a good job again."
Willian may have put in a man-of-the-match display but the Brazilian knows he has to maintain that level as Chelsea's season reaches a crucial stage.
The Blues now face back-to-back trips to Manchester, facing United - and old boss Jose Mourinho - on Sunday before heading to champions-elect City the following weekend.
"It was one of my best performances here,' added Willian. "I almost had a hat-trick!
"We were a bit unlucky but we must be proud of our performance because we played really well.
"To play against Barcelona is not easy and now we have to think about the other games.
'We go there in three weeks' time and we have difficult games as well in the Premier League. Now we have to think about the games coming and then we have to think about Barcelona."