The Chelsea legend highlighted the performances of Ander Herrera and Michael Carrick as key in the goalless draw on Thursday night.
Lampard felt that his old boss Jose Mourinho, now in charge of United, played for the point in order to keep his side’s chances of a top four finish intact.
‘I’m slightly surprised. We did feel that he was going to defend deep,’ the 38-year-old told Sky Sports.
‘They definitely played for that. They didn’t over-commit players at any stage. I think Martial played like a left-back at times.’
Lampard felt that United’s midfield, lacking the injured Paul Pogba, was crucial to the result, although he did single out Marouane Fellaini for criticism.
The Belgian was sent off with six minutes to go at the Etihad after a reckless headbutt on City forward Sergio Aguero.
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‘I give real credit to the midfield – not to Fellaini for what happened at the end – Michael Carrick and Ander Herrera worked their socks off,’ Lampard added.
‘When you look at the table, maybe you see why they played for it, as the top four is in their hands still.
Manchester United fixtures
Swansea (H) – Sun 30 April
Celta Vigo (A) – Thu 4 May
Arsenal (A) – Sun 7 May
Celta Vigo (H) – Thu 11 May
Tottenham (A) – Sun 14 May
Southampton (A) – Wed 17 May
Crystal Palace (H) – Sun 21 May
‘I don’t think Mourinho wanted to go toe-to-toe with Manchester City tonight. He looked at the bigger picture.
‘They got the result they wanted, and they’re happy in the dressing room, for sure.’