WHAT IT MEANS: Apologies to Seinfeld’s Cosmo Kramer, but there’s a new “K-Man” in town.

Mets rookie right-hander Matt Harvey struck out nine Rockies in six innings on Wednesday night, and now has 43 in his first six career appearances, the most in franchise history, according to ESPN Stats & Information. Nolan Ryan had 42, though one of his appearances was in relief.

Harvey K’d five of the first six batters he faced and carried a no-hitter into the fourth before Jonathan Herrera broke it up with an opposite-field single leading off the frame. It was one of three hits allowed by Harvey, who also went 2-for-2 with a pair of singles at the plate and is hitting .455 (5-for-11).

Harvey, who gave up one run, walked two and picked up a no-decision, was lifted after throwing 102 pitches, and righty reliever Ramon Ramirez proceeded to give up a leadoff homer to Wilin Rosario in the seventh, which snapped a 1-1 tie. Later in the frame, DJ LeMahieu executed a perfect suicide squeeze that brought home Tyler Colvin and gave Colorado a two-run lead.

The Rockies won, 5-2, at Citi Field. The Mets (57-67) have now lost four straight, 13 of their past 15 at home and are 11-27 since the All-Star break.

Scott Hairston (first-inning sacrifice fly) and Ike Davis (eighth-inning RBI single) accounted for New York’s offense. The Rockies capitalized on Kelly Shoppach’s throwing error and plated two insurance runs off Frank Francisco (6.42 ERA) in the top of the ninth. The Mets brought the tying run to the plate in the bottom half, but Ronny Cedeno flew out to deep left to end the game.

BOO THAT MAN: Jason Bay went 0-for-3 with two strikeouts and was hastily booed after each of his failed plate appearances. He’s batting .148 on the season, and has five hits in his past 56 at-bats. With the tying run aboard at first and two outs in the eighth, Bay was lifted in favor of pinch-hitter Jordany Valdespin, who struck out to end the frame.

NO MORE JO: Johan Santana isn’t expected to pitch again this season after being placed on the 15-day disabled list with inflammation in his lower back.

UP NEXT: Right-hander Collin McHugh, 25, makes his MLB debut on Thursday afternoon against Rockies right-hander Tyler Chatwood (3-3, 5.46 ERA).