The former Sauber driver took over driving duties from team-mate Jenson Button for the second day of the Jerez test.
He completed 81 laps and ended with the seventh fastest time, 1.354 seconds off pacesetter Romain Grosjean's Lotus.
"Today was a great day. Since I drove it out of the garage and did the first laps, I knew that this car has good potential," he said when asked for his impressions on driving a McLaren for the first time.
"The feedback was good straight away and you definitely feel [the car's potential]. We don't know how competitive we are but all I can say is that the car feels good.
"We managed to do some good programmes, so hopefully we can keep doing the same in the next five days [of testing] and we will be in good shape ready for the start of the season."
The 23-year-old, who signed his deal to switch teams in September last year, was thrilled to have taken the wheel of a McLaren for the first time.
He added that the preparation work that he had done made it much easier to adapt to his new surroundings.
"Oh, a lot of excitement," he said when asked how he felt on his first run in the MP4-28.
"There has been a lot of simulator [work], a lot of preparation for this day.
"This is what you are looking for: to get into the car, to start working with the engineers, to debrief and start spending hours trying to improve yourself.
"Finally the day came and I am very happy."
Perez was surprised by how different the cockpit accommodation was in the McLaren compared to the Sauber.
The Mexican plans to make some small tweaks to the car, but overall was pleased with how well he fitted in.
"It's much more different than I expected just by sitting in a different seat," he added.
"It's so different that you have to adapt yourself to a different position, a different way to hold the steering wheel; pretty much everything is different. It's like starting from zero.
"I'm happier than I was expecting today. I still need to sort out some things to be a bit more comfortable but, even so, we managed to do an incredible day."
F1 editor Edd Straw
It's going to take a while to get used to seeing Sergio Perez in the silver of McLaren rather than the colours of Sauber. The man himself summed it up best when he used the word "different" when chatting about his first day in the car at McLaren.
With Lewis Hamilton inadvertently stealing the headlines today thanks to his brake problem-induced crash, Perez had the chance to play his way in gently.
Judging by his happy demeanour after the chequered flag flew, even when confronted with a larger contingent of media than he used to get back in his Sauber days, the experience of driving a McLaren grand prix car absolutely lived up to his expectations.
There will be far tougher days ahead for Perez, but all the signs are that he is already relatively comfortable in his new environs and far from overawed.
But as the man himself said, "the team expects a lot from me." A solid first day is the least of those expectations and there is still much to be done.