CHICAGO -- Saturday afternoon. Sellout crowd at Wrigley Field. The youngest Mets starting pitcher since Dwight "Doc" Gooden in 1985 on the mound. Yeah, there was something a little extra special about the Mets' game against the Cubs. However, in a lineup featuring five rookies, it was more apparent than ever that the club is playing for the future.

The Mets' Jenrry Mejia made his much-anticipated debut as a big league starting pitcher, battling through five up-and-down innings in a 5-3 loss to the Cubs in front of 39,473 at Wrigley Field.

"I thought he started pretty good. He showed some promise," said Mets manager Jerry Manuel. "He had good command early. I thought the breaking ball was better for him [the first] time around [the Cubs' batting order].

"I thought the second time around, they made some adjustments to him. In order for him to get deep into games, he's got to be able to throttle that. I think that'll come with time."

Mejia (0-3) became the seventh Mets pitcher to start a game at the age of 20, the last being Gooden a quarter-century ago. He made some big pitches in runners-on-base situations, but he was more shaky than dominant, striking out two and walking two in his five innings. That echoes his performance in 30 relief appearances, when he struck out 17 and walked 15 in 27 2/3 innings. Mejia struck out right about a batter an inning during his four-year Minor League career.

Considering his inexperience, was Mejia nervous before the game?

"No way," he said, putting that notion to rest.

It was once common practice for a big league manager to break in young starters by working them out of the bullpen, and Mejia's calm demeanor may not be that surprising considering the time he spent in the Majors as a reliever earlier this season.

"Because of the experience he had here before, a lot of the anxiety wore off," Manuel said. "What I'm looking for him is being able to manage a game vs. veteran hitters the second and third time around.

"I thought he did OK, but there are some things he needs to take command of to become what you'd consider to be a solid, solid player."

Mejia departed after allowing a pair of runs in the fifth inning. In that fifth, he gave up a single to Chicago's Starlin Castro, who then swiped second off Mejia and fellow rookie Mike Nickeas, who made his big league debut at catcher. He came home on Marlon Byrd's single. Mejia recovered to get Aramis Ramirez and Xavier Nady, with Nady's flyout to center advancing Byrd to third base. Mejia struck out Tyler Colvin -- another rookie -- with a pitch in the dirt that got away from Nickeas. Colvin made it to first safely on the wild pitch as Byrd raced home, putting Chicago up, 4-1.

Mejia retired the first four Chicago hitters of the game before giving up a one-out second-inning single to Nady, who scored one batter later on Geovany Soto's double. Mejia walked Blake DeWitt intentionally, then allowed an infield single to opposing pitcher Carlos Zambrano. However, Mejia escaped further damage by getting Kosuke Fukudome on a grounder to second baseman Luis Castillo.

Mejia said that he threw as well as he did in the Minors, but the hitters are just better at the game's highest level.

"There are better hitters at the Major League level. I threw the same [pitches]," said Mejia. "I threw a couple of curveballs to [Soto] and he got a hanging one, but I'll keep working at it."

Mejia also allowed a run during a third inning that could have been worse. Byrd singled with one out and advanced to third on Ramirez's double. He scored on Nady's sacrifice fly to left. Mejia threw the first of two wild pitches with Colvin at the plate, moving Ramirez to third. But Mejia recovered to get Colvin on a chopper to first, ending the threat. Overall, Mejia burned through 96 pitches in five innings, 64 for strikes, in his first outing since being sent to the Minors to work on polishing has arsenal.

"I thought he commanded his offspeed pitch better than when he left here," said Mets pitching coach Dan Warthen. "As far as velocity, he didn't work at 100 percent, but moved it up when he wanted to."

Mejia came in with supposed improved command of his secondary pitches, and while he had just one unintentional walk, he got behind a few hitters and left some pitches up in the zone. The three lefties in the Cubs' lineup -- Fukudome, Colvin and DeWitt -- went 1-for-8 against Mejia, but all five Cubs runs and all four RBIs were tallied by right-handed hitters.

"I still think what we see is a young pitcher that still has the tendency to get the lefties out, but has trouble getting the righties," Manuel said. "And [the Cubs are] a veteran right-handed-hitting ballclub."

The Mets got two runs in diametrically opposed ways, first with their legs, then with the brawn. With one out in the fourth and runners on first and third, rookie Lucas Duda struck out, but Carlos Beltran beat Soto's throw at second on the back end of a double steal as Castillo scored at the front. Castro, the Cubs' shortstop, appeared to be a bit late covering the second-base bag on the double steal, which irked the temperamental Zambrano.

"I talked to Castro after that play and he apologized to me," Zambrano said. "I said, 'It's OK.' I was a little upset. He should make that play. It's good when a veteran on this team, you apologize or say something to a young guy -- he's still in the process of learning things in the big leagues."

The play didn't derail Zambrano (7-6) too badly in a sharp outing in which he allowed just two runs on four hits over seven innings. He struck out Mets cleanup hitter David Wright looking in the sixth, bending him backwards on a looping curveball that registered 64 mph on the radar gun and dropped into the strike zone.

"That's a slider. He just does whatever he wants up there. I called for a normal slider and he threw it slowly," said Soto. "I buckled, too. I called it and I'm waiting for a normal slider, and I saw it up and I buckled."

The brawn came in during the seventh, when Mets rookie first baseman Ike Davis lofted a fly ball that got into the wind tunnel blowing out to right field and landed in the bleachers for his 16th home run and his first since July 29, when he went deep against St. Louis' Blake Hawksworth at Citi Field. Davis went 101 at-bats between homers.

The Mets added a run in the eighth. Castillo reached on a two-out walk, and Beltran followed with a blast to the ivy in center. Byrd backed up to the wall and leaped, but the ball popped out of his glove. Beltran strolled into second with a double, scoring Castillo with his second run of the game and drawing the Mets to within two runs. It was Beltran's third hit of the game, marking just his second three-hit game of the season.

Flamethrowing Bobby Parnell came out of the Mets' bullpen and lit up the radar gun with triple digits on a few offerings and got the Mets out of a jam in the eighth. After a walk and a single chased Mets reliever Pedro Feliciano, Castro sacrificed, moving the runners into scoring position. Parnell walked Byrd intentionally, but escaped the jam by striking out Ramirez and Nady. In the ninth, the Mets got a one-out single from Davis, but Cubs closer Carlos Marmol struck out Duda, rookie Josh Thole and pinch-hitter Mike Hessman, all looking, to preserve the win.

With the Mets now four games under .500 (66-70) and well back in the playoff chase, the last month of the season is very much about getting a jump on the future. To that end, Mejia will take make another start, likely on Friday when the Mets return home for a weekend series against the Phillies.

"We've got to see him again, because if you can bring that kind of stuff along, then you got a good piece for the future," said Manuel.