On a night on which the Phillies could have moved into first place in the National League East with a win, Eflin didn't have his fastball command, and the Blue Jays took advantage of it.
The Phillies (28-20) remain a half game back of the Atlanta Braves, who lost at Boston, 6-2.
In 4 2/3 innings, Eflin allowed six runs (five earned) on nine hits. The righthander had seven strikeouts and walked just one.
Most of all, he was hurt by a rare first-inning hiccup.
Toronto scored three first-inning runs on Teoscar Hernandez's RBI single and run-scoring doubles by Yangervis Solarte and Kevin Pillar.
How rare was that?
In his three previous starts this season, Eflin had not surrendered a run and had only allowed two hits in the first three innings.
All of Toronto's first inning runs came with two outs.
"It was tough," Eflin said of that first inning. "Obviously I kind of slipped away from my rhythm in the first inning. But it's baseball. It happens."
That is a good way to explain Eflin's first career home run, a 418-foot blast to center field. It really happened.
That was the first homer by a Phillies starting pitcher since Sept. 5 2017, when Ben Lively hit one against the New York Mets.
"It is hard to hit a no-doubter home run to center field here," Phillies manager Gabe Kapler said. "And the moment it left his bat everybody thought it was a home run."
Eflin had a natural reaction to his first career homer.
"Any time you can help the offense out in any way you can is fun as a pitcher," he said. "It does give you a little extra motivation to go out there. You're amped up a little bit. It gets some adrenaline going."
The adrenaline and momentum didn't last when Eflin allowed three runs in the fifth, extending Toronto's lead to 6-1. The big blow was Justin Smoak's two-run homer to left-center, a shot that went almost as far Eflin's blast, traveling 414 feet.
Smoak got everything from Eflin's 93-mph two-seam fastball on a 1-0 count.
That pitch was an example of the difficulty Eflin had all evening with his fastball command.
"The fastball command wasn't really there where I wanted it to be," he said. "I thought I threw some pretty good secondary pitches."
Getting behind in the count also hurt Eflin.
"At the end of the day I kind of fell behind some hitters, and a bunch of stuff happened, and I kind of got in trouble and lost rhythm a little bit," he said.
Despite his struggles, Kapler found something positive about the performance.
Eflin "did a really good job keeping us in the game without his best command," Kapler said, although some may debate that allowing six runs in 4 2/3 innings is keeping a team in the game. "He fought to give us some length, and we needed it from him."
Ever the optimist, Kapler says he saw some encouraging signs.
"I think he had his stuff. I think he had the life on his fastball," Kapler said. "I am just not sure he had the ability to put it where he wanted like he normally does."