The ball was soaring toward right field, hooking toward the corner, and pinch-runner Alexi Casilla was absolutely certain it was going to drop.
So he took off from first base with one out and the Baltimore Orioles trailing Boston 5-4 in the bottom of the ninth.
"Bad read," Casilla would say later, not too long after he was doubled up to end Saturday's game.
There were plenty of other reasons the Orioles lost, among them an uneven performance by starter Freddy Garcia, Baltimore's inability to build on an early lead and a blown call by home plate umpire Jeff Nelson.
"It's a game where all the little things add up at the end," catcher Matt Wieters said, "and we fell just short today."
Most glaring, however, was Casilla's baserunning blunder.
After Wieters hit a two-run homer off Andrew Bailey to get Baltimore within a run, Casilla broke from first base on a liner by Ryan Flaherty. Shane Victorino made the catch without much difficulty and threw out Casilla for the double play.
"Flaherty hit that ball very good," Casilla said. "He crushed it over my head. I kind of started running and looked where Victorino was playing and thought no chance he was going to catch that ball."
Mike Carp and Jonny Gomes homered to help Boston extend its lead over second-place Baltimore in the AL East to 2 1/2 games.
After dropping the first two games of the series, the Red Sox fell into an early 2-0 hole before bouncing back. Carp's home run snapped an 18-inning scoring drought in the fourth, and Gomes made it 5-2 in the sixth with a solo shot that chased Garcia (3-4).
Every starter except for Jarrod Saltalamacchia got at least one hit, including two by Gomes. Boston finished with nine hits, four for extra bases.
"Us getting shut out's not going to last too long," Gomes said. "We've got some pretty good hitters on this team."
Including Carp, who's been pressed into action at first base since Mike Napoli fell ill in the third inning of Thursday night's game. Napoli was sent back to Boston on Saturday so team doctors can determine why he's been feeling groggy over the past few days.
Carp insisted that the Red Sox didn't come into the game thinking about their offensive funk.
"We feel like we're going to mash every day," he said. "It just takes one guy to get going, fortunately today it was me. Tomorrow it's going to be another guy and so on and so forth."
The Red Sox lost three games at Camden Yards last September and were 0-2 this season, their longest dry spell in Baltimore since a seven-game stretch in 1969-70.
Lackey (4-5) gave up two runs, seven hits and a walk in seven innings to improve to 12-4 lifetime against the Orioles. It was the right-hander's first win since May 25, even though he's allowed three runs or fewer in nine of his 11 starts this season.
Former Oriole Koji Uehara struck out the side in the eighth and Bailey got three outs for his eighth save.
Baltimore's Manny Machado extended his career-high hitting streak to 13 games and hit his major league leading 31st double. Despite the loss, Baltimore has won 13 of its last 18 games against the Red Sox.
The Orioles took a 2-0 lead before Lackey got an out. After Nate McLouth singled off the pitcher's foot and scored on a double by Machado, Nick Markakis singled and Adam Jones drove in a run with an infield hit. Lackey avoided further damage by retiring Wieters and J.J. Hardy with runners at second and third.
"It might have been the key to the game," Boston manager John Farrell said.
David Ortiz led off the Boston second inning with a liner to center that bounced off the wall and eluded Jones. The husky man known as "Big Papi" legged it out for his second triple this month; the last time Ortiz had two triples in a season was 2006.
With Ortiz on third, Carp drew a walk before Garcia got three straight outs.
The Red Sox ended their season-high scoring drought with a three-run fourth. After Dustin Pedroia singled and Carp homered to tie it, Gomes singled and Stephen Drew ended a 4-for-31 skid with an RBI double.
Pedroia's single came after Nelson ruled he fouled off a third strike. In reality, Pedroia missed it.
"It was a break for us," Pedroia said. "I just said `I thought I fouled that.' Then he said, `Foul ball.' I thought I hit something. It was probably the ground. I don't know."
Boston made it 4-2 in the fifth. Jacoby Ellsbury led off with a single, his first hit in 12 at-bats during this series. He stole second, advanced on a bunt and scored on Pedroia's grounder to shortstop.
Baltimore put runners at the corners with no outs in the bottom half, but Lackey worked out of the jam.