SAN DIEGO - Twenty two pitches into his major-league career, Jake Thompson glanced at the Phillies dugout and saw his new pitching coach, Bob McClure, coming toward him. Thompson, 22 and wide-eyed, arrived here as a touted prospect. The game humbled him within minutes.

"Kind of typical," Phillies manager Pete Mackanin said, "for a guy in his debut."

Thompson's introduction Saturday night, a 9-7 loss to the Padres, was not memorable. He allowed four first-inning runs to a mediocre San Diego lineup and could not survive five innings. He walked more (two) than he struck out (one). He hit a batter. He threw a wild pitch.

"I wasn't nervous," Thompson said. "I was kind of amped up instead of being nervous. Especially in that first inning, I just wasn't able to spin the ball for strikes or be able to get fastballs down in the zone."

"He's 22 years old," Mackanin said. "You can't judge him on this outing."

There will be another day for Thompson, one of the key pieces acquired from Texas in the Cole Hamels trade last summer. The rebuilding Phillies brought him here for the remainder of the season to learn about life as a big-league pitcher.

He has much to discover.

Thompson permitted six runs. He could not locate his slider, and in the first inning, he abandoned his trademark sinker - the pitch that guided him to groundouts and success in the minors.

With one out in the fifth, Mackanin emerged to grab the ball from Thompson. He will start again Friday at Citizens Bank Park, and just like fellow 22-year-old righthander Zach Eflin, Thompson has almost a week to dissect an inauspicious debut.

This rout featured some oddities, like Padres pitcher Paul Clemens wearing a No. 91 jersey with "PLAYER" on the back and Cesar Hernandez trying to steal third base with a four-run deficit in the seventh inning.

Well, one of those things was unexpected.

"I have no idea why he went," Mackanin said of Hernandez's ill-fated attempt, which marked his 13th out made on the bases this season. The manager added: "He's got so much talent. We have to corral it and figure out a way to get him on track."

No one expected immediate greatness from Thompson. He joined Eflin, Severino Gonzalez, Ethan Martin, Rafael Quirico, and Turk Farrell as the only Phillies pitchers to allow six or more earned runs in five or fewer innings for their debuts.

The Phillies envision Thompson as a presence in the middle of their future rotation. He was not known in the minors for an overpowering arsenal, but rather an effective and economical one. On Saturday, he did not resemble that pitcher.

Thompson threw 30 pitches - 16 of them fastballs - in a 20-minute first inning. Catcher Cameron Rupp and he tried to establish his slider, a swing-and-miss pitch when executed well, but an inadequate one when up in the zone.

"He threw a ton of breaking balls," Mackanin said. "He hung three or four curveballs and slider up in the zone. Maybe he thought he couldn't throw his fastball in the big leagues. Who knows? He's 22 years old."

Thompson admitted he threw a few more breaking pitches than usual.

"I was also having a little bit of trouble trying to miss a few bats and get some outs," he said. "I just didn't have great command."

Travis Jankowski attacked Thompson's first pitch, a 91-mph sinker, and slashed it to left to start the inning. Thompson never settled. He wasted little time between pitches, a frenetic pitcher with plenty of jitters. As he released every pitch, he used such force that it almost pushed him off the Petco Park mound.

The first three Padres reached on a single, walk and single. Thompson retired the next two on a line out and a strikeout. Ryan Schimpf walked. Then, Christian Bethancourt cleared the bases with a scorched double to center.

That brought McClure to the mound to calm his rookie. After McClure's visit, Thompson fired two fastballs. He jumped ahead, 0-2, to Alexei Ramirez. He induced a groundout to complete his first inning, but not until the eighth pitch of the at-bat to Ramirez.

Thompson may not make it to the end of the season; the Phillies have limits on all of their young starters and Thompson reached a career high in innings pitched between the minors and majors with his outing Saturday.

Until then, he searches for major-league lessons, not all of which will be like the hard ones experienced in his debut.