Jayson Stark reacts to the Red Sox's acquisition of Drew Pomeranz for 18-year-old Anderson Espinoza, who Stark says has been compared to Pedro Martinez. (1:01)

BOSTON -- Say this for the Boston Red Sox: They're going for it in David Ortiz's final season.

With the finish line in sight for their retiring franchise icon, the Red Sox didn't wait for the Aug. 1 trade deadline to get help for an inadequate rotation. President of baseball operations Dave Dombrowski didn't spare all of the organization's top prospects either, acquiring All-Star left-hander Drew Pomeranz from the San Diego Padres for touted 18-year-old right-hander Anderson Espinoza on Thursday night in an old-fashioned, one-for-one trade between clubs with vastly different timelines for contending.

The Red Sox, who return from the All-Star break in a three-way fight for the American League East crown, get a pitcher who appears to be coming into his own at age 27 but has already reached his big league career high in innings pitched this season at 102. Meanwhile, the 38-51 Padres get an elite prospect who has been compared to a young Pedro Martinez but probably won't sniff the big leagues until at least 2019.

"I'd rather trade three [lesser]-type guys than Anderson, but that wasn't appealing to San Diego," Dombrowski said. "They really wanted more of the focus of the premium guy. There's always risk with pitchers, no matter how old they are. We know that Drew hasn't thrown this many innings. We think he can handle it. We also know there's a risk in Anderson, a young pitcher that we like a great deal."

Dombrowski said Pomeranz is scheduled to make his Red Sox debut Wednesday at Fenway Park against the San Francisco Giants.

To make room for Pomeranz on the 40-man roster, infielder Josh Rutledge, who is out with an injured left knee, was transferred to the 60-day disabled list.

Espinoza, ranked No. 14 on ESPN Insider Keith Law's midseason top 50 prospects list, was one of the most gifted arms in a Boston farm system that hasn't produced a homegrown starter since Clay Buchholz in 2007. But with the demand for pitching far outweighing the supply of available starters -- and the Baltimore Orioles and Texas Rangers, fellow AL contenders, equally desperate for pitching -- the cost was always going to be exorbitant. Dombrowski had little choice but to act quickly and pay a steep price.

"Sometimes if you have more supply than demand, you're in a position; if you wait [until the trade deadline], sometimes it can be beneficial," Dombrowski said during a conference call. "But in a case where the demand exceeds the supply, which is definitely the case in this situation, I'm not sure you don't take a greater risk by waiting, because demand continues to build. I don't think there's a lot more guys becoming available. We had a pretty good pulse of that."

Left-hander Drew Pomeranz, a first-time All-Star this season, joins a Red Sox team that sits just two games behind the Orioles in the AL East standings. Andy Hayt/Getty Images

Pomeranz's value has been built almost entirely over the past three months. A first-round draft pick of the Cleveland Indians in 2010, he earned his first All-Star selection this season after posting a 2.47 ERA and allowing 67 hits and 41 walks in a career-high 102 innings over 17 starts for the Padres. He ranks second in the majors in both opponents' batting average (.184) and opponents' OPS (.555).

Before this season, though, Pomeranz bounced between the rotation and the bullpen for the Colorado Rockies and the Oakland Athletics, posting a 4.60 ERA and allowing 240 hits and 106 walks in 228⅔ innings as a starter. The lefty has now been traded four times.

But the Red Sox are betting on Pomeranz being a late bloomer because he has started throwing a cutter this season. They believe Pomeranz's cutter has made his fastball more effective because he doesn't have to throw it as frequently. In the past, he was primarily a fastball-curveball pitcher.

Pomeranz will join a rotation that includes ace lefty David Price, upstart knuckleballer Steven Wright and right-hander Rick Porcello. Red Sox starters have posted a 4.72 ERA in the first half, which ranks 19th in the majors.

Boston needed a fourth starter The Red Sox's top three starters -- David Price, Rick Porcello, and All-Star Steven Wright -- have performed OK this season. The back end of the rotation, however, has been a disaster. Top 3 starters* All others W-L 30-13 7-12 ERA 3.59 7.22 K-BB 331-91 117-84 *Price, Porcello, Wright -- ESPN Stats & Information

The final two spots in the rotation have been a black hole, with six pitchers combining for a 7.22 ERA. The Red Sox are hoping lefty Eduardo Rodriguez, 23, has corrected mechanical flaws that contributed to an 8.59 ERA in six starts since he came off the disabled list in late May, but they also can't bank on a significant improvement from him.

"We have four guys, and we're hopeful Eduardo steps up at this point when he pitches on Saturday [in New York against the Yankees]," Dombrowski said. "And we'll see what else happens beyond that."

Hired in August with a win-now mandate from owner John Henry, Dombrowski has lived up to his reputation as an aggressive wheeler-dealer. In November, he acquired closer Craig Kimbrel from the Padres for four minor leaguers, including touted outfielder Manuel Margot and infielder Javier Guerra. He also signed Price and veteran outfielder Chris Young and traded for reliever Carson Smith in a span of about three weeks during the offseason. Within the past week, he has made four trades, acquiring veteran infielder Aaron Hill, utility man Michael Martinez, reliever Brad Ziegler and now Pomeranz.

Espinoza was widely regarded as the Red Sox's top pitching prospect and third-best prospect overall, behind second baseman Yoan Moncada and center fielder Andrew Benintendi, both of whom are playing at the Double-A level and could reach the big leagues later this season before Ortiz exits the stage.

Espinoza is still years away from the majors. And after dominating the rookie-level Gulf Coast League with a 0.68 ERA and 40 strikeouts in 40 innings last season, he has struggled against older competition in the low-Class A South Atlantic League. In 17 starts for Greenville, he has notched a 4.38 ERA and given up 77 hits and 27 walks in 76 innings.

The Padres were able to pry away Espinoza because Pomeranz isn't eligible for free agency until after the 2018 season. Pomeranz is making only $1.35 million this season, his first year of arbitration eligibility.

Dombrowski noted the comfort of knowing Price, Wright, Porcello and Pomeranz would be locked up beyond this season.

"We found we were being asked for the same people no matter what the amount of service time left was," Dombrowski said. "Even though somebody was in the last year [until] free agency versus somebody that had a couple of years to go, the same names that kept coming up, the players that we were being asked to trade."

Trading Espinoza was also slightly more palatable for the Red Sox because of the re-emergence of right-hander Michael Kopech, who has returned from last year's drug suspension and a broken hand in spring training. One Red Sox official said last week that Kopech has "the best arm I've ever seen," and in a start for Class A Salem on Wednesday night, Kopech threw a pitch that was clocked at 105 mph.

The Red Sox were also on the verge Thursday night of signing first-round draft pick Jason Groome, a touted high school left-hander who figures to take Espinoza's place as a prized pitching prospect.