Porto striker Benni McCarthy admits he was unimpressed with Manchester United's display in the first-leg of the Champions League knockout stages a fortnight ago where the South African scored twice to give his team a historic 2-1 victory over the 1999 UEFA Champions League winners.
The South African international grabbed a brace for the Portuguese champions as they had to come from behind to beat United 2-1 at Estadio De Dragao after compatriot Quinton Fortune had given the Premiership champions the lead.
But McCarthy has revealed he was "surprised" that his side were able to dominate proceedings in Portugal and he was "disappointed" that the Red Devils had given such a poor performance.
"I was shocked by our spirit compared to them," he told BBC Sport. "I kept it secret that as a child I was a United supporter. I was surprised and disappointed that they were not like the team I had grown up watching.
"We managed to completely outplay them, which was a big surprise to me."
The 26-year-old will once again line-up against Sir Alex Ferguson's men on Tuesday in the second-leg at Old Trafford and the forward is confident Porto can overcome their opposition away from home as they are unbeaten on foreign soil in Europe's premier club competition.
Porto have only lost one game in Europe this season - the 3-1 home defeat by Real Madrid in October - and the former Celta Vigo hitman believes his side learned an important lesson from that loss.
He added: "Real Madrid have the upper hand over Manchester United. They're very consistent and they're playing well almost every game and not dropping points. They also have the edge over United in that they have more big-name players, which intimidates other teams.
"When you play against Real you are sometimes scared to even tackle. It automatically gives them the upper hand and teams tend to respect them too much.
"That was a lesson we learnt. We were not going to respect United on the field, only after the game. That was the difference as to why we beat United and not Real.