TORONTO -- Brad Keller was at his best in July, flashing the type of stuff that made him an above-average pitcher through his first three seasons as a Royal. But on the day the calendar flipped, Keller flopped; and an injury forced him out early, to boot.

Keller was pulled with lower back tightness after just three innings in the Royals’ 5-1 loss to the Blue Jays on Sunday afternoon, which completed a three-game sweep for Toronto. It was deemed “precautionary” by the team.

Keller noticed something wrong while warming up in the bullpen, saying that his back “locked up” on him. As someone who has dealt with tightness like that before, he was hoping it’d subside over the course of his start.

“And for some reason, this time it just never really loosened up,” Keller said.

The 26-year-old right-hander navigated the first two innings fine, allowing a pair of harmless singles, but the Blue Jays blitzed him in the third.

The first four hitters reached safely, highlighted by Marcus Semien’s two-run homer, and three of those hits came with an exit velocity of 102-plus mph. After Keller fanned Bo Bichette in the next at-bat, manager Mike Matheny came to the mound with trainer Nick Kenney to check on him.

Matheny noticed that Keller was no longer following through properly on his pitches. Keller said he was OK, though, and stayed in to finish the frame two batters later. But with that, his day was finished, too.

“Maybe that was just adrenaline taking over,” Keller said of his lobbying to stay in the game. “I think that’s anybody’s competitive nature, just keep going no matter what’s barking or what’s hurting.”

Keller’s focus, despite his own ailment, was to try to go as deep as possible into the game. It’s something he’s done steadily for most of the season, as Sunday snapped a 15-start stretch in which he pitched five or more innings. He worked into the seventh in all four July starts, posting a 2.28 ERA and a .194 opponent batting average.

The next steps toward getting healthy and getting back on the mound are already underway. Keller received treatment after exiting the game and said afterward that his back was much looser. Rest and muscle relaxers will be important in the coming days, and it’s still too early to tell if he’ll miss any time.

“Hopefully it goes away before next start,” Keller said.

The Royals’ run of eight wins in nine games came to a crashing halt with this sweep, which opened their three-city road trip on a sour note. They averaged 5.1 runs per game during their hot streak, before scoring just five runs in the three games against Toronto.

Sunday’s game offered its chances, as Kansas City had traffic on the basepaths in five of the first six innings -- including a bases-loaded opportunity in the sixth.

Andrew Benintendi doubled, after which Hunter Dozier and Michael A. Taylor were hit by pitches to set the table for Edward Olivares. But Olivares swung through a patented sweeping curveball from José Berríos, ending the threat.

Berríos and his curveball are no strangers to the Royals, who saw him regularly during his five-plus seasons with the Twins. In fact, Kansas City’s hitters had gotten the better of him recently, tagging him for a 5.32 ERA over eight starts since 2019. But with his new team in his new home ballpark, Berríos was simply better.

Olivares came through with a solo homer in the ninth, snapping Kansas City’s 17-inning scoreless drought and preventing back-to-back shutouts. But the Royals will need far more than that from their offense if they want to get back in the win column on this road trip.

Monday’s off-day can serve as a reset, but then comes a three-game set against the White Sox. The Royals did just top the Sox in three of four at home, but the AL Central leaders are never an easy foe.

“We’ve got some tough games ahead of us,” Matheny said. “So hopefully we can put this one behind us and get back to playing really good baseball.”