Atlanta Braves' Jason Heyward (22) initially beats the tag but slides past the base and is tagged out by Dustin Pedroia (15) during the eighth inning of a baseball game on Monday, May 26, 2014, in Atlanta.

ATLANTA - There's a troubling trend developing on baseball's best pitching staff.

Ervin Santana is in a rut.

Santana couldn't hold a five-run lead in his third straight poor start as the Atlanta Braves fell to David Ortiz and the Boston Red Sox 8-6 on Monday.

The defending World Series champions snapped their 10-game losing streak as Ortiz homered and drove in four runs. Santana has a skid of his own to worry about after giving up at least five runs for the third straight start.

The Braves began the day with a 2.78 earned run average -- best in the majors. Atlanta starters also led MLB with their 2.82 mark, but Santana's has climbed to 4.06 after he allowed six runs on five hits and three walks in five innings.

"I felt pretty good the whole game," Santana said. "A couple of mistakes and that's how it is."

Santana gave up a three-run homer to Ortiz in Boston's five-run fifth. The rally began with a two-out walk to pinch-hitter Daniel Nava, a double by Brock Holt and another walk to Xander Bogaerts.

"Two quick outs, and then after that I just lost my control and made a couple bad pitches and they took advantage of it," Santana said.

Braves manager Fredi Gonzalez said he stuck with Santana because of his track record.

"He's a guy that's been pretty darn good for you. Try to give him a chance to get the win there," Gonzalez said. "He's a veteran guy that you would think would know how to wiggle through the lineup, but that inning just unraveled on him."

Dustin Pedroia drove in two runs with a single before Ortiz tied the game with his homer.

With Red Sox fans at Turner Field chanting "Papi! Papi!" the World Series MVP then gave Boston the lead with a bases-loaded sacrifice fly off Ian Thomas (1-2) in the seventh.

"It seems like every big situation we need him, he came through for us," Pedroia said of Ortiz.

Boston Red Sox outfielder Jackie Bradley cannot reach a 2-RBI double hit over his head by Atlanta Braves' Justin Upton during the third inning of a baseball game on Monday, May 26, 2014, in Atlanta, Ga.

Ortiz hit only .118 with no RBIs in Boston's longest losing streak in 20 years, but that didn't dim his star appeal to Red Sox Nation South. The roar following his homer startled A.J. Pierzynski, who was waiting on deck.

"When David hit that homer, that was probably the loudest cheer as a visitor I've ever heard, especially since I was on deck and sort of got the full force of it," Pierzynski said.

"It was one of the loudest moments I can remember in any stadium."

The Red Sox trailed 6-1 after the fourth, with starter Clay Buchholz walking a career-high eight batters in only three-plus innings.

Buchholz has a 7.02 ERA after allowing six runs, and Boston manager John Farrell said "there's no determination" about the right-hander making his next start.

Justin Upton drove in three runs with two hits for Atlanta.

Edward Mujica (2-1) got the win with a scoreless sixth inning following an hour-and-a-half rain delay.

Chris Johnson singled with one out in the ninth before Koji Uehara capped his 10th save with Andrelton Simmons' game-ending double-play grounder. Uehara was Boston's seventh pitcher.

Following the rain delay, Thomas walked two batters following an infield hit by Holt, loading the bases. Ortiz drove in Holt with a fly ball to right field, giving Boston a 7-6 lead. Pierzynski's single up the middle pushed the lead to two runs.

Jason Heyward led off the Atlanta eighth with a single to center field off Andrew Miller but slid past second base trying for a double. He was tagged out by Pedroia while reaching back for the bag.

Braves right-hander Aaron Harang will pitch against the Red Sox and lefty Jon Lester tonight.