The Rangers capped a magnificent month with Hamilton's game-ending two-run, two-out double as a pinch-hitter after starting May with a loss for a 7-15 record that was the worst in the American League.
"Felt like in April, we had water in the gas tank," first-year manager Jeff Banister said. "Stopped the car, it kept running ... when you went to start it and push on the gas it (sputtered). We had to get a tuneup, and we had some guys that really have found that rhythm."
At 26-25 to open June, the Rangers are above .500 for the first time since being 31-30 last June 6 in a season that ended with an AL-worst 95 losses.
Credit the offense for the turnaround from April, along with some shuffling in the bullpen.
Texas hit a majors-worst .210 the first month, and scored only 75 runs.
The Rangers scored more than twice as many runs in May, when .359 hitter Fielder started going deep again (nine homers after only one before that), Shin-Soo Choo batted .295 for the month (after .096 to start the season), rookie Delino DeShields had an AL-high 10 stolen bases and Hamilton rejoined the team a week ago.
"Talent-wise, we have such amazing guys, and we're just going to get better," shortstop Elvis Andrus said. "We have to maintain what we've got right now, and just build on it."
The Rangers, with Monday off to start June after only one off day in May, have won 19 of their last 29 games and four series in a row. They took three of four games from Boston over the weekend for their first series win at home.
Hamilton, who homered twice Saturday and didn't start Sunday for the first time in his seven games since getting back, delivered the game-winner in a 4-3 win to wrap up his first home series for Texas since 2012.
"You never know what can happen, and that's what Ranger baseball is all about," Hamilton said on the field postgame, after he and Fox Sports Southwest field reporter Emily Jones were doused by the contents of two water coolers.
In the clubhouse a few minutes later, Hamilton said he was reminded of "some good times for the Rangers."
Hamilton was the 2010 AL MVP, a five-time All-Star and part of their only two World Series appearances with Texas from 2008-12 before leaving in free agency to the AL West rival Los Angeles Angels. He was traded back to the Rangers on April 27, four weeks before his season debut.
"Whether or not it's coming back to a place of comfort where he's had success, he looks more sure of himself," Red Sox manager John Farrell said before Sunday's game. "I don't know that I saw the same type of swings at any time that he was elsewhere. ... He looks to be playing with a lot more confidence."After World Series closer Neftali Feliz gave up three runs in the ninth inning of a 10-8 loss May 16, Banister said the next day there were no longer any set roles in a much-maligned bullpen. Since then, Shawn Tolleson has pitched in game-ending situations and converted all six of his save chances.
"Early on, we had some starts that we didn't take advantage of," Banister said. "We have the capability of taking advantage of some of the starts we're getting now."
For at least the next two weeks, though, the Rangers will be without Adrian Beltre. The third baseman sprained and cut his left thumb sliding into a base Sunday. Texas called up top prospect Joey Gallo, who is hitting .314 with nine homers and 31 RBIs in 34 games for Frisco. All nine of his homers have come in the past 23 games.