It typified the frustration that has become the Rangers' season.
Gagne threw 11 pitches and had two strikes on Pedroia before giving up the home run, the first of the season for an opponent against the Texas reliever. He entered the game with a 0.00 ERA.
It also came on the heels of Otsuka surrendering two runs in the eighth to give the lead back to the Red Sox. Otsuka had not allowed an earned run in his previous seven outings, lowering his ERA to 1.02.
"I really felt good about our chances today," said Rangers manager Ron Washington. "You wouldn't think Aki would give up two and Gagne a bomb.
"They're only human. They've been flawless up to this point. There's no reason to think this is going to be a trend."
Prior to Sunday, the Rangers were 14-0 when leading after the sixth inning, a statement to the performances of Otsuka and Gagne. Texas led 4-3 after seven, scoring all four runs in the sixth, highlighted by a three-run home run by Mark Teixeira.
In a yeoman effort, Teixeira made the Rangers' record books with his blast of 453 feet. It was the fourth longest in Ballpark history, the longest being Jose Canseco's 480-foot blast on June 13, 1994.
"We felt comfortable right there," Washington said. "That's baseball. You can't predict it."
Pedroia's home run, only his second of the season, came on a fastball down the middle.
"Right now, I care about getting wins," Gagne said. "Always try to have the mind-set that you don't want to give up runs.
"Like I've said the past six years, it's good to have a save because you get a win."
Boston took the lead on Mike Lowell's one-out RBI single. Earlier in the eighth, J.D. Drew -- who was 2-for-4 after entering the game 0-for-15 on the road trip -- tied the game with an RBI single.
The Red Sox took a 3-0 lead in the fourth when Jason Varitek hit a three-run homer off Rangers starter Kameron Loe, who was looking to snap a four-game losing streak. He left after six innings.
"Kam always leaves his heart out there, and he did today," said Washington. "Too bad we didn't get the win for him."
Pedroia's blast put the Red Sox up, 6-4. The Rangers closed the gap with an RBI single by Teixeira in the bottom of the ninth, but Sammy Sosa flew out to center to end the game.
The win gave the Red Sox a sweep of their three-game series against the Rangers, their first at The Ballpark and only their second in Arlington. They won three at the old Arlington Stadium on Aug. 20-22, 1973.
The Red Sox and Rangers continued down completely different paths with Sunday's Boston win. The Red Sox own the best record in baseball at 34-15, only the fifth time they've been that good after 49 games. Texas, on the other hand, at 18-32 and losers of five straight, has the second-worst record in the Majors (Kansas City is 18-33).
"I've been 14 games out before and won it [a division]," Washington said.
"We're going to keep fighting.
"I keep saying we're right there, but every night I come in here [the media interview room] and we've lost a game."
Loe and Young echoed their manager's thoughts on the Rangers not giving up on the season.
"We do still have four months left," Loe said.
Young, in fact, made reference to a neighbor of the Rangers from down south as a possible inspiration for the team to turn its season around.
"Houston's record when they went to the World Series in 2005 was similar to ours," Young said.
Then he added that the performances of the Rangers' two top relievers Sunday was a most unusual situation that opponents need not count on.
"Given the same situation [in future games], I like our chances," Young said.