Goals from Anthony Martial and Scott McTominay helped United seal a 2-0 victory over the champion to remain in fifth place and extend its unbeaten run in all competitions to 10 games, Reuters reported.
“There’s a long way back but it was a huge step. I’ve given City huge praise over the last few years ... but I felt like it meant more to United than City,” Keane told Sky Sports.
“They’ve been under a lot of pressure and criticism. I’ve been critical, but United have done well. It’s a big boost for Ole. The atmosphere was fantastic. But when you get a big win you have to follow it up.”
Keane’s ex-United teammate and fellow analyst Gary Neville hailed United’s first home and away league double over City in a decade.
“It still doesn’t give them what they want in terms of a Champions League place or a top-four finish, but something like that was a big moment,” Neville said, praising midfielders McTominay, Fred, Nemanja Matic and Bruno Fernandes.
“I was thinking about the midfield and universally United fans would say it’s been pathetic for 18 months... all of a sudden United have a midfield when it had been nonexistent.
“Are they the best group of United players that have been here in the last eight years? No, not for a talent. But they’re a far easier group to like because they want to be here.”
United visits LASK in the last 16 of the Europa League on Thursday before a league trip to Tottenham Hotspur on Sunday.