SAN DIEGO -- Matt Harvey is not the type of pitcher who keeps to himself before games. In the hours prior to his third career start, Harvey strolled amiably around Petco Park's visiting clubhouse, doling out handshakes, high-fives and back-slaps to his teammates. He continued to look and act like a big leaguer.But for all Harvey's maturity, for all his presence, he is still just 23 years old. He has made just three big league starts. As a result, he is prone to inconsistency. With that in mind, Harvey shed his aura of invincibility on Sunday, as the Mets knew he eventually would. Coming off two starts that were every bit as good as his team could have anticipated, Harvey gave up five runs to the Padres over five innings at Petco Park, dropping the Mets to a 7-3 loss. "Obviously he's frustrated because he wants to win," catcher Rob Johnson said. "He wants to put up zeros and give us every chance to win. And he's out there to do that." Lacking the same type of fastball command that he showcased against the Giants last week, Harvey served up a two-run home run to Chase Headley on a changeup in the first inning, then another two-run shot to Yonder Alonso on a middle-in fastball in the third. He also gave up Carlos Quentin's RBI double in the third inning, digging the Mets a five-run hole. "When I tried to go away, it was either six inches away or six inches middle," Harvey said. "It was one of those days where I couldn't find the strike zone, and when I did, it was not quality. I wasn't executing the way I had the last two starts." To their credit, New York's hitters fought back, plating two runs on Ronny Cedeno's pinch-hit homer off Padres starter Jason Marquis in the sixth inning, and another when Jason Bay greeted former teammate Dale Thayer with a sacrifice fly in the seventh. But the Mets could not rally against the back end of San Diego's bullpen. Marquis, a New York native who was often linked to the Mets in Hot Stove rumblings the past few winters, allowed only those three runs over 6 1/3 innings. And the Padres later scored some insurance on Quentin's homer off Ramon Ramirez in the seventh. But the Mets lost their best chance at victory early, when Harvey could not keep the league's 30th-ranked offense in check. "He has a power fastball. ... We knew he was going to throw it," Alonso said. "We knew he was a guy that liked his fastball and he was going to be around the plate. We were hopeful that he was going to leave them up and [we could] put good swings on them." To be certain, the rookie's outing was not entirely a loss, with Harvey displaying much of the same potential that made him successful over his first two big league starts. After giving up a leadoff triple to Will Venable in the second inning, for example, Harvey mowed down the next three batters on two popups and a strikeout to strand Venable at third. Harvey repeated the trick two innings later, putting runners on the corners with no outs before setting down the next three Padres on an unsuccessful squeeze bunt and two strikeouts. He struck out five in total and walked one, giving him 23 whiffs and seven free passes over his first three starts, a span of 16 1/3 innings. Crediting his middle-inning improvement to a mechanical adjustment that pitching coach Dan Warthen suggested, Harvey also demonstrated an ability to adjust on the fly. Rather than continuing to "collapse" his back side as he delivered his pitches, Harvey stayed upright and began throwing at a more downward angle, allowing him to improve his command. He retired six of the final seven batters he faced. "As soon as he said something," Harvey said of Warthen, "it was pretty evident to me that I was doing it." And that is why in some ways, Sunday's outing was Harvey's most promising yet. Lacking his best swing-and-miss stuff, and certainly lacking his command of it, Harvey showcased an ability to adapt. He also demonstrated plenty of self-awareness in dissecting his outing, explaining why things went wrong instead of simply rehashing the fact that they did. Then he vowed not "to change anything because of one bad start." For a young pitcher, those are all rare traits that can only help him in the future. "He realizes that his stuff's good," manager Terry Collins said. "He knows that. He realizes now that he's got to locate it."