Goals in either half from Anthony Martial and Maguire secured the points for Ole Gunnar Solskjaer's visitors, with Maguire adjudged not to have kicked out at Michy Batshuayi after a tussle on the sideline.
Lampard said he felt the England international defender should no longer have been on the pitch in order to score his side's clinching second goal.
"Maguire should get a red and then he scores a second goal. The game changes off that.
"That was a major part of what VAR was brought in for, a second viewing, different angles. The referee can’t see all the angles, and if you’re not going to look at the monitor then you’re definitely not going to see it.
"It’s harder to take with the presence of VAR than it would have been before. That is what it was brought in for. It’s very confusing when all the different angles still bring the wrong decision. It’s universally a wrong decision. It could be my opinion, but everyone I’ve spoken to, not just in our dressing room, but neutrals have said the same.
Kurt Zouma had a goal disallowed for Chelsea in the second half for an adjudged foul in the build-up on Brandon Williams, while Olivier Giroud saw a well-taken header also ruled out for a marginal offside call by the video technology.
Lampard thought the first of those goals should have been counted.
"The Zouma goal should have stood. At first I didn’t think it should, it looked like a shove from Azpilicueta, but when you see it again he gets shoved in the first place. It certainly wasn’t clear and obvious. And Giroud was offside."
However, unsurprisingly, United boss Solskjaer disagreed and felt the Video Assistant Referee had a good night on the whole.
“You want the right decisions to be made and we’re happy they were made, because they weren’t being made without that help. It’s been shown a few times this year that we’ve needed that help. I don’t know why that is. [The Giroud goal], that’s offside. [For Zouma’s goal] I just looked at the screen and it looks like a push in the back. So, for me, that’s not a goal.”
The Norwegian also said it was only right that Maguire remained on the pitch.
“I wouldn’t think that’s a red card. He’s just protecting himself. He’s got a lad [Michy Batshuayi] standing over him and he’s got his legs where it does hurt.”
The result means United do the double over their west London rivals for the first time ever in the Premier League, with the gap now closed between the pair to just three points.
United next take on Club Brugge in their Europa League last-32 first leg on Thursday night, before a home Premier League tie against Watford on Sunday.
Solskjaer says it's going to be a quick turnaround for his team.
“It gives us confidence and it gives us a chance. It’s going to be a tight race; we’re not going to get help from anyone because we played tonight and we’ve already got a game on Thursday night [in the Europa League]. I cannot, for the life of me, understand why we didn’t play on Saturday. We’ll just have to dust ourselves off and get going again, and recover as quick as we can.”
