ST. LOUIS -- Brayan Bello was hoping to spend his 25th birthday pitching the Red Sox out of their recent rut.

But his normally trusty changeup betrayed him in that quest, as the righty gave up five runs on seven hits over 4 2/3 innings.

He also tied a career high by giving up three homers in his team’s 10-6 loss to the Cardinals in Friday night’s opener of a three-game series at Busch Stadium.

“The changeup wasn’t good for him tonight, so it was tough for him to get some swings and misses,” Red Sox manager Alex Cora said. “It felt like the slider was better than the changeup. He grinded through it, gave us [almost] five. I think if you look at the outing, the damage was done on the changeup. He felt like he never had the feel for it tonight.”

The numbers back that up.

Of the 28 changeups Bello threw, the Cardinals swung at 13 of them and had just three whiffs, hitting the pitch at an average exit velocity of 101.1 mph.

“The changeup wasn’t there today,” Bello said. “When I was trying to throw it into the dirt, it was staying to the middle.”

Lars Nootbaar was the first one to capitalize on Bello’s inability to command one of his best pitches, as he deposited a 2-1 changeup to straightaway center for a quick 2-0 lead for the Cardinals just two batters into the bottom of the first.

The most frustrating part of the performance for Bello was the inability to hold St. Louis at bay after the Red Sox tied the game twice. When the Red Sox came back to tie it at 2 in the second on David Hamilton’s two-run triple, Bello gave the lead right back when his sinker was belted out of the yard by Nolan Gorman in the bottom of the inning.

The Red Sox fought the good fight on offense in this one. Rafael Devers hit an equalizing missile to center field for his third homer in as many nights, a shot that went a Statcast-projected 443 feet. Career homer No. 179 for Devers allowed him to pass Nomar Garciaparra for sole possession of 12th on the team’s all-time list.

Again, though, Bello couldn’t keep fortune on his side. Alec Burleson mauled a Bello changeup for a solo shot in the fourth to put St. Louis back on top -- this time for good.

“It was a bad outing,” said Bello. “The team did everything possible to score runs. They gave me some run support, but I wasn't able to make the adjustment tonight, and it was a bad outing for me.”

At 22-23, Boston is below .500 for the first time since after the third game of the season. The Sox are 4-10 since May 2.

“One game under .500,” said Cora. “It’s not a big deal. You win the series here and you’ll be over .500.”

For the second straight night, a Boston pitcher finished with exactly 100 pitches without making it through the fifth inning. Bello (4 2/3 innings) did last longer than Cooper Criswell (3 2/3 innings), but that was of small consolation for Boston.

While the offense has largely been the culprit of the team’s recent struggles, the bats have scored five or more runs in each of the past two games while the pitching -- the team’s strength all season -- has given up 17 runs in those two games.

“They did OK,” Cora said of his offense. “At the end, we were 3-for-12 with men in scoring position. The at-bats are getting better, which is a positive out of the game.”

As for Bello (4-2, 3.96 ERA), this was his second start after coming off the injured list. He had been sidelined from April 21 through May 12 with right lat tightness.

“I felt very good,” Bello said. “Just a bad outing. Once in a while, you're going to have one of those, and today was one of those and there's still a lot of outings for me, a lot of starts for me.”