The 36-year-old, who is on a six-month loan at the Premier League champions from New York City, was well received by the away end as he came on to replace Aleksandar Kolarov during the sides' meeting at the Etihad Stadium on Sunday.
The hosts were trailing 1-0 thanks to an Andre Schurrle strike and had been reduced to 10 men after Pablo Zabaleta picked up a second yellow card for a trip on Diego Costa.
But Lampard - Chelsea's record goalscorer - made an almost instant impact on proceedings, guiding home a brilliant volley to steal a share of the points for Manuel Pellegrini's men with five minutes of normal time remaining.
And, after the game, Lampard admitted that the day had been a "difficult" one, but insisted he had to remain professional when called upon by his manager.
"It's a really difficult one. I'd be unprofessional if I didn't come on and do my job," he told Sky Sports.
"I tried to get back in the box, it was a great ball from Milly [James Milner]. I had 13 amazing years with Chelsea fans. So I'm mixed with it.
"Obviously, I'm really pleased the team I play for got a draw, so it a really hard one for me to answer.
"I'm a bit lost for words. I didn't expect to come on and score like that. I come on and the Chelsea fans are signing and that's emotional, then I'm playing for this club who have taken me in brilliantly as well.
"So I'm really stuck in the middle here. I didn't know what I wanted from today, it was a tough one. I suppose this can be seen as a happy medium at the end.
"It's a long season, and these two teams, plus others will fight on, it'll make for an interesting Premier League."
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