PHILADELPHIA -- Near the end of his pregame media session at Citizens Bank Park on Monday, Giants manager Gabe Kapler decided, unprompted, to steer the conversation toward rookies.

Most of Kapler’s spiel focused on center fielder Wade Meckler, who enjoyed a meteoric rise to the Majors this year but is already enduring his share of growing pains with San Francisco.

“I think we can expect that some of those struggles are just part of the learning process,” Kapler said. “Talking a little bit about Meckler now, I don’t think the competition is what has been a real challenge for him so far as much as a little bit of nerves and a little bit of adjusting to pitching styles.”

But Meckler’s struggles at the plate bled into his defense on Monday night, with San Francisco's No. 11 prospect committing a pair of costly misplays in center field in a 10-4 rout at the hands of the Phillies.

The Giants got early solo shots from Joc Pederson (first inning) and LaMonte Wade Jr. (third), but they couldn’t capitalize on a bases-loaded opportunity in the first frame against right-hander Aaron Nola, who escaped by getting Johan Camargo to bounce into an inning-ending double play.

The Phillies outslugged them from there, launching four blasts -- including an inside-the-park homer by Bryce Harper in the fifth inning -- to power a commanding win in the opener of this pivotal three-game series between the two National League Wild Card contenders.

Meckler badly misjudged Harper’s Statcast-projected 405-foot drive off the angled center-field wall, forcing him to chase after the ball when it ricocheted toward right field. Once he reached the ball, Meckler bobbled it twice before throwing to the infield, allowing Harper to zip around the bases to complete his inside-the-park homer, the second allowed by the Giants in the past week.

“My thought was it was a ball I could catch,” Meckler said. “I thought I had a play on it. By the time I realized I didn’t have a play on it, it was off the wall. Then I was just chasing it down, trying to stop him from scoring, and I didn’t pick it up clean.”

Meckler wasn’t charged with an error on that play, but he did receive one in the first inning, when he bobbled a single by Trea Turner, allowing the Phillies’ shortstop to advance to second and later score on Harper’s two-out base hit off opener Scott Alexander.

Those miscues were part of an all-around poor defensive showing for San Francisco. Shortstop Camargo and third baseman Wilmer Flores also committed errors, while left fielder Blake Sabol allowed Johan Rojas’ line drive to go over his head for a two-run triple that ignited a four-run rally for Philadelphia in the seventh.

With their 11th loss in their past 15 games, the Giants (65-60) sank to the third NL Wild Card spot, slipping three games behind the Phillies (68-57) and a half-game behind the Cubs (65-59) with 37 games left. San Francisco still leads Philadelphia, 3-1, with two games remaining in the season series, a key advantage considering head-to-head records are now the first tiebreaker in the standings.

“We don’t want to dwell on one [game], particularly one that didn’t go well,” Kapler said. “I don’t think there’s much to look back on, other than we probably don’t want to do it the same way again in the next couple of games.”

Left-hander Sean Manaea, who relieved Alexander, gave up the Phillies’ first two homers while working 2 2/3 innings, marking the first long balls he’d surrendered since May 17. Rookie Sean Hjelle was also hit hard, giving up six runs on 10 hits over 4 2/3 innings.

Meckler and Hjelle could be candidates to be optioned on Tuesday, when the Giants will have to clear a pair of roster spots for left-hander Kyle Harrison, who will be called up for his Major League debut, and right-hander Ryan Walker, who will be activated off the paternity list.

San Francisco was hoping Meckler could provide a jolt to its offense after batting .379 across three Minor League levels this year, but the 23-year-old’s elite hit tool hasn’t translated to the Majors yet. He’s gone just 3-for-21 with 13 strikeouts and two walks over his first seven games.

“It’s pretty obvious that he’s battling right now,” Kapler said. “He’s battling in every capacity. Obviously, it’s not good enough, and it’s not helping us win baseball games. But at the same time, this is when a coaching staff throws their support behind a young player.”