WHAT IT MEANS: Matt Harvey has a promising career ahead of him, but undoubtedly also will suffer through some growing pains.

Harvey surrendered two-run homers to Chase Headley and Yonder Alonso and departed after five innings, having surrendered five runs.

The Mets ultimately lost to the Padres 7-3 on Sunday afternoon at Petco Park. They completed their three-city NL West road trip with a 6-5 record after the rubber-game loss in San Diego.

Harvey's line: 5 IP, 8 H, 5 R, 5 ER, 1 BB, 5 K, 2 HR, 81 pitches (50 strikes).

He became only the second visiting pitcher this season to surrender two homers at spacious Petco Park, joining Colorado’s Drew Pomeranz.

MARQUIS MATCHUP: After surrendering a game-opening single to Ruben Tejada, Jason Marquis retired 14 straight batters. Marquis actually faced the minimum through five innings. (Tejada was erased attempting to steal.)

Mike Baxter, who walked a franchise-record-tying five times Saturday, reached on a base on balls to open the sixth to end Marquis’ streak. Ronny Cedeño, pinch-hitting for Harvey, then delivered a two-run homer to pull the Mets within 5-2.

It was Cedeño’s second career pinch-hit homer. He also accomplished the feat April 6, 2007 with the Cubs against Milwaukee’s Claudio Vargas at Miller Park. It was the eighth pinch-hit homer for the Mets this season. Jordany Valdespin has five and Scott Hairston two.

The Mets had ended Marquis’ 2011 season two weeks after he was acquired by Arizona from Washington at last year’s trade deadline. Angel Pagan’s line-drive comebacker broke the fibula in Marquis' right leg. Marquis continued to pitch, but collapsed an inning later while delivering a pitch to Josh Thole.

BAY WATCH: Jason Bay contributed a seventh-inning sacrifice fly after ex-Met Dale Thayer replaced Marquis, which pulled the Mets within 5-3. But the left fielder otherwise went 0-for-2 before departing on a double-switch.

Bay hit .065 (2-for-31) on the road trip. He may start Tuesday with the Mets facing a southpaw, Miami’s Wade LeBlanc. Bay’s playing time figures to seriously diminish against right-handed starters, though.

Meanwhile, Ramon Ramirez surrendered a pair of late runs as the Padres opened a four-run lead.

WHAT’S NEXT: After a team off-day Monday, Jose Reyes and the Marlins visit Citi Field. Jon Niese (8-5, 3.72 ERA) opposes LeBlanc (1-1, 1.35) in Tuesday’s 7:10 p.m. series opener. Reyes takes a career-high 24-game hitting streak into the series. Tejada has a career-high 11-game streak intact.

By Tuesday, the Mets should have a verdict on the extent of Tim Byrdak’s left shoulder injury. They also should know whether Kirk Nieuwenhuis, who has a tear in the plantar fascia in his right foot, will require surgery.