SAN DIEGO -- As it turns out, Drew Pomeranz's first All-Star Game appearance was also his last at Petco Park as a member of the Padres.
San Diego dealt the 27-year-old left-hander to Boston on Thursday. The Padres, who sold high on Pomeranz after a brilliant first half, will receive 18-year-old right-hander Anderson Espinoza, who instantly slots into their system as the No. 1 prospect.
Pomeranz is coming off a first half in which he posted a 2.47 ERA -- tied for third in the Majors. His .184 batting average against is the best in the National League.

"Not an easy guy to deal," said general manager A.J. Preller. "Any time you have a left-handed starter that's performed the way he has -- and the resulting All-Star berth -- you've got to feel very good about the return that you're getting."
In short, the Padres do, indeed, feel very good about that return. Preller said Espinoza was "close to untouchable" from a trade standpoint. He boasts a fastball that can touch 98 mph while sitting in the mid-90s. On top of that, Espinoza has a curveball and a changeup that could potentially become well-above-average out pitches.
"It says a lot to Espinoza what the guys in our group thought about him," Preller said. "From that standpoint, when we looked at it, we felt like we were getting a premium guy, a guy that's been close to untouchable in the last year."

Pomeranz, who amassed 102 innings for San Diego in the first half, has never hit the 150-innings mark. His previous Major League high was 96 2/3, with Colorado in 2012, a season in which he also threw 50 2/3 frames in the Minors. He can become a free agent after the 2018 season.
Espinoza, who was given a $1.8 million bonus to sign with Boston during the 2014-15 international signing period, went 5-8 with a 4.38 ERA for Greenville of the South Atlantic League this season.

The Pomeranz deal is just the latest route through which the Padres have stocked up on young pitching talent in the last month. They traded closer Fernando Rodney for 20-year-old right-hander Chris Paddack in June before signing top international pitching prospect Adrian Morejon out of Cuba.
Of course, those signings came after the Padres used 10 of their first 12 Draft picks on pitchers, including Stanford's Cal Quantrill at No. 8 overall.
"You start to feel the excitement from the player development staff," Preller said earlier this month when asked about the influx of prospects.
"They're seeing talented players and guys that they feel have a chance to come up here and impact at Petco. That's big. ... When you get these guys all on the field together, that's what we've been building for."
The trade marks the fourth time Pomeranz has been dealt since being drafted No. 5 overall in 2010. The Padres acquired him from the A's during the offseason in exchange for first baseman Yonder Alonso and reliever Marc Rzepczynski. (San Diego also received Minor Leaguers José Torres and Jabari Blash in that deal.)
The Padres have clearly made a solid return on their investment in Pomeranz. But for now they need to replace him, and Preller named reliever Paul Clemens and Triple-A righty Edwin Jackson as immediate options. The trade could also clear room for Michael Kelly, who has flown through the system this season, appearing at all three levels.
"That's the challenge for our scouting group as well," Preller said. "Find the next Pomeranz. Find somebody that, with some opportunity, has some ceiling.
"There's huge value in depth, there's huge value in numbers. I think we saw a lot of value in getting these guys together in the next few years. ... In the Minor Leagues, here in the next year or so, every day when you look up, there's going to be a pitcher on the mound that's got a chance to be impactful."
It's not the first time Preller has dealt with Boston's Dave Dombrowski. Last November the Padres sent Craig Kimbrel to Boston in exchange for four prospects -- two of whom, Manny Margot and Carlos Asuaje, debuted at Petco Park during Sunday's SiriusXM All-Star Futures Game.
Preller enjoys working with Dombrowski, but would he compare himself with Boston's president of baseball ops?
"Definitely not in the way I dress," Preller quipped. "That would be a major compliment, because he's pretty sharp that way.
"But baseball-wise, he's easy to deal with, honestly. He's straightforward, he's a guy that's direct. That's the way that we've approached things in the last couple years. He's a guy that's willing to trade value for value."
The Padres certainly had value in Pomeranz, an All-Star lefty. Now they think they have value for years to come in Espinoza.