LAKELAND, Fla. — Matt Harvey had a little extra juice when he needed it Monday.

After watching his fastball lag to start the Grapefruit League season, the Mets right-hander threw a series of pitches that registered 95, 96 and 95 mph in the third inning, according to the radar gun at Joker Marchant Stadium.

This represented progress for Harvey, even on a day he surrendered three earned runs on seven hits with four strikeouts over 4¹/₃ innings against the Tigers in the Mets’ 5-1 exhibition loss.

Harvey’s final line took a beating in the fifth inning, when he surrendered three singles and two runs as he was building up his pitch count to 74.

“I guess everybody has been talking about [velocity], and it was nice to go out there today and kind of dial it up a little bit into the mid-90s,” said Harvey, who maintained a fastball in the 93-94 mph range most of the game. “I was excited after the last start — I kind of felt a lot better on the mound and that I could let it go, and the past bullpen [session] it felt real good, so definitely a positive move for me.”

Harvey, who is returning from surgery for thoracic outlet syndrome, has appeared in four games this spring and pitched to a 7.30 ERA. In his previous start, against the Marlins on Wednesday, his fastball sat mostly in the low 90s.

“The best stuff I have seen so far,” manager Terry Collins said, referring to Harvey’s performance Monday. “We were looking at two big keys today. One was maintaining his delivery, and the second was better command, and we saw both.

“Today his velocity picked up, but he maintained his velocity. I thought that was very important, to be able to go [74] pitches and still be at 93, 94, so those were keys for me.”

Harvey is expected to pitch twice more in the exhibition season, with the goal of getting his pitch count close to 100. And it probably wouldn’t hurt if he received results to back up his improved stuff.

James McCann’s homer in the second had accounted for the Tigers’ only run until Harvey allowed three singles in the fifth that helped sink the Mets into a 3-0 hole.

“What happened in the fifth inning, I don’t want to have happen during the regular season,” Harvey said. “Building up your arm strength there, it’s kind of a stepping stone. Obviously the first three steps didn’t go as planned, but I felt this one was a big step forward. Not making the fifth inning happen is just building up arm strength and we have two more starts down here and then the regular season.”

Harvey suspects he’s tried to muscle his fastball too much this spring, after needing that extra effort last season, when he struggled to a 4-10 record with a 4.86 ERA in 17 appearances before he was diagnosed with thoracic outlet syndrome in July.

“Kind of having bad habits last year of really having to fight my arm through being weak, tired, I really had to put a lot of effort into it,” Harvey said. “I think just getting used to being out there and really not having to over-muscle things is definitely the biggest step from the last three starts to this one. The ball was coming out pretty smooth and I was able to throw harder if I wanted to or take a little bit if I wanted.

“I felt like throwing 95, 96 today was a good start and definitely something to work off.”