BOSTON -- A day off the injured list, Edwin Jackson summed up his mindset for the remainder of the 2019 season.

"Free," he said prior to Monday's game against the Red Sox.

Jackson returned from the IL on Sunday after being sidelined since June 18 because of a lower back strain. The 35-year-old right-hander adopted a positive attitude during his time off. For as much baseball as he has played, Jackson views the second half of his 17th Major League season as a clean slate.

"When I was away, I kind of just took a breath and relaxed and went out with the approach [of], 'It's a new start,'" Jackson said.

The Blue Jays are utilizing Jackson out of the bullpen for the time being, and he made his return from injury in the fifth inning of Monday's 10-8 loss to the Red Sox. He pitched three scoreless innings, with three hits, one walk and a pair of strikeouts.

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"It was good to be back out there," Jackson said after the game. "Obviously the outcome wasn't what we wanted, but it feels good to be able to repay the bullpen a little bit and help pick them up in a situation where they needed me to pick up some innings."

Jackson's stint was his longest scoreless outing since Aug. 11, 2018, when he pitched 7 1/3 innings against the Angels as a member of the Athletics. Holding the Red Sox without a run in the fifth, sixth and seventh innings helped set the Blue Jays up for a four-run eighth-inning comeback attempt after the Red Sox plated 10 runs in the first three innings.

"He was throwing harder, he was throwing more strikes and his slider was pretty sharp," Blue Jays manager Charlie Montoyo said of Jackson. "He did a great job. He kept us in the game. We needed those innings, and he gave us three good innings."

The Blue Jays acquired Jackson from the Athletics in mid-May, making Toronto his record-setting 14th big league team. Prior to going on the IL, Jackson made five starts for the Blue Jays. He pitched out of the bullpen following an opener in his last two appearances, going 1-5 overall in the first half of the season. In Jackson's previous outing, he allowed seven runs (including three homers) in two-thirds of an inning against the Angels on June 17.

Jackson is coming off a 2018 season in which he went 6-3 with a 3.33 ERA, the third-lowest ERA of his career, in 17 starts with the Athletics.

"[I] just want to get back and revert to having fun like I was last year," Jackson said. "Obviously, I know what I can do. I would be at home if I didn't think that I could do it. But [I want to] just go back to having fun, and whatever's going to happen, let it happen."

Jackson rehabbed with the Class A squad in Dunedin, Fla., and then the Triple-A team in Buffalo before being cleared to return. He missed being around his Blue Jays teammates for 21 games and embraced the atmosphere of camaraderie when he returned to the clubhouse.

"I was getting healthy," Jackson said. "Also, just kind of getting back to finding myself again and having fun with the game. This is a game that we play, so sometimes we take it too serious and kind of forget the have-fun aspect of the game."

What does having fun look like for a player who is placed in high-pressure situations each time he steps on the mound?

"You're not thinking. I think that's the biggest thing when you're having fun as a baseball player," Jackson said. "You're going out, you're letting the game come to you, you're allowing it to happen. When people are going good, you don't know what you're doing, you're just kind of doing it.

"Once things start going bad, you kind of start searching. Or you feel everything and you start to get too mechanical and you start to get -- I like to call it -- too smart for your own good, because we all know what we want to do. Sometimes we overthink the process instead of taking a step back and let it happen."

When Jackson made his 402nd big league appearance on Monday, he did so with a renewed outlook. He said he was more anxious in his return than he expected to be, and he looks forward to settling in for the rest of the season.

After all, there's a lot more games left to simply have fun playing baseball.

"Our worst day on the field is someone's dream," Jackson said.