The Blues are seeking a fifth FA Cup triumph in seven years, with 2011 winners City standing in their way at Wembley and eager for silverware after effectively relinquishing their Barclays Premier League title to champions-elect Manchester United.
"It's a tournament that's been pretty good to us," Lampard said.
"We've just performed very well and we've got good success. That can change the minute you don't perform so well.
"Against a team of Man City's quality, you can't take any positives from previous history.
"If they're at their best, we're below our best, they'll probably win the game, and vice-versa. You're talking about two very good teams.
"We've got a lot of respect for them and I think it will be a good match, especially if both teams are at their best. You'll see a proper Wembley semi-final."
Lampard highlighted City's threats across the pitch, particularly Carlos Tevez, Sergio Aguero, Yaya Toure and David Silva and believes Chelsea's opponents will be boosted by their Premier League win at Old Trafford on Monday.
"There's a few key threats for them," Lampard said. "Tevez is a fantastic player. I love his energy and his quality. He's always a threat and he's done it against us a few times.
"Aguero, what he did the other night (scoring against United), speed off the mark, his ability.
"I think they'll probably be on a high from their last result in the league, but other than that I think it's an even start with two good teams."
England midfielder Lampard has plenty of personal experience of Wembley, with all four Chelsea triumphs in recent years coming at the redeveloped national stadium.
But he is uncertain if he will be selected having played the full 90 minutes of Thursday night's 3-2 defeat to Rubin Kazan in Moscow which saw the Blues edge through to the Europa League semi-finals 5-4 on aggregate.
Chelsea play Basle in the last four with the first leg in Switzerland.
Chelsea's congested fixture schedule means interim boss Rafael Benitez must rotate his squad and Lampard, while insisting he is ready, has no complaints.
"I've been lucky enough to play in a lot of great finals for Chelsea, at Wembley and elsewhere," added Lampard, who could be in the final weeks of his 11-year spell at the club.
"We've had some success there. I've had success at Wembley with England and Chelsea.
"I'm not sure I'll be playing on Sunday. I don't think anyone's an automatic selection for the manager at the minute as we see, because there's lots of games and he's changing it regularly.
"I'm like everyone else - I want to play every game but it's not possible."
Lampard played down any possible impact of the trip to Moscow, with Benitez is expected to make numerous changes from what was a poor performance, particularly defensively.
"On paper they'll be fresher than us, but we've come off the back of qualifying for a semi-final," Lampard said.
"We're all professionals and we're all fit lads. I won't be using that as an excuse going into the game."
Chelsea's tumultuous season has been under close scrutiny and subject to criticism, yet last season's European Cup winners could finish the campaign on a high with two trophies still to play for, while they are well-placed in third in their bid for Champions League football next term.
Like the Blues, City have under performed this term.
City's defence of their Premier League title has been limp as United have marched towards the trophy, but Lampard will not be underestimating them.
"We're both pretty high-profile (clubs) now," he said.
"We've been high-profile for a good few years with the injection of Roman Abramovich and I think Man City are starting to get used to that kind of profile as well.
"I've seen some people be quite negative about them this season because they set a level last year that they want to stick to.
"It's been quite difficult this year for a lot of teams because Man United have been very, very consistent in their results in the league. That's what has let them pull away.
"We all know that Man City are a top, top, football team."