It was Tolleson's fourth blown save of the season. He only had two last season.
"I don't think I have had a slump like this in my career," Tolleson said. "It's frustrating. Our guys battled all game long and I gave up a big home run. They are counting on me to get three outs and I didn't get it done."
The Rangers had taken a 5-4 lead in the top of the ninth on a two-out, two-run home run by Ian Desmond.
"That's not a ballgame you want to lose," Rangers manager Jeff Banister said.
Tolleson has allowed seven runs on three home runs in his last two outings. He has a 9.20 ERA on the season and opponents are hitting .343 off him. It was about this time last season that Banister pulled Neftali Feliz out of the closer's role and went with Tolleson.
He was outstanding in the role but now Banister is once again concerned about his closer.
"I definitely have a level of concern," Banister said. "That's one I'm not ready tonight to make a decision on. Obviously his fourth blown save, it's a challenge. We've got to be able to make pitches and end the game ... close the game out after we fought back and took the lead."
Tolleson had two days off after allowing three runs on Saturday. Sam Dyson closed out Sunday's win against the Blue Jays.
"I was pretty fresh," Tolleson said. "Everything was good. I felt good physically."
The rally started on a questionable play. Stephen Vogt led off the inning with a little roller down the first-base line. Tolleson fielded it and threw to first but the throw hit Vogt. He was safe on the play. The Rangers thought Vogt was running inside the base line and should have been called out but the play is not reviewable.
"They told me he was in the lane," Banister said. "Their judgment, their call."
"I was trying to make a play anyway I could," Tolleson said. "A lot of those situations, you're taught to throw at the runner. I was just trying to get him out."
Coco Crisp followed with a double down the right-field line, putting runners on second and third. Tolleson then got Billy Burns on a popup to Rougned Odor and the Rangers walked Josh Reddick to load the bases.
Tolleson then got Danny Valencia to pop out to shallow right, leaving him one out away from escaping the jam. But he had to go through Davis, who had already hit two home runs.
Both were on off-speed pitches. Tolleson went with six straight fastballs. Davis took two for balls and then fouled off three. Davis hit the sixth one over the left field wall.
"He had already hit two on off-speed pitches so I was trying to beat him with the fastball," Tolleson said.
"Tolly trusted his fastball and just missed location," Banister said. "Center-cut fastball. Something you can't do in that situation."