Belisle was holding on to a 4-3 lead with two outs and the bases loaded in the fifth when Sosa tattooed an 0-1 cutter up and over the plate. It quickly cleared the fence for a grand slam and gave Sosa 599 career home runs -- one short of the esteemed 600 plateau.
"It was just too fat of a pitch, and he hit it out of the ballpark," Belisle said. "An unacceptable pitch in that situation. If I'm going to get beat, it needs to be with my best -- or at least in a better spot."
The Reds' third consecutive loss dropped their record to 26-42, just a half-game from the 25-42 Rangers and the burden of the Majors' worst record.
"What do you want me to say, '[We] quit'? We're not going to quit," said left fielder Adam Dunn, who hit a two-run homer in the bottom of the fifth to keep Cincinnati close. "This is our job, just like anyone else's. And we're going to try to take pride and play hard and finish what we started."
Both teams' bullpens each provided four scoreless innings, with Eric Gagne shutting the door to notch his seventh save for Texas. Todd Coffey was a bright spot for Cincinnati, with 1 2/3 scoreless innings.
But the damage had already come early and often in this one.
Belisle (5-5), who allowed seven earned runs and nine hits over five innings with one walk and five strikeouts, started decently. Through four innings, he gave up a first-inning RBI single to Sosa and Ramon Vazquez's two-out solo homer in the second inning while striking out the side.
With Rangers starter Vicente Padilla (3-8) responsible for six earned runs and 12 hits in his five innings, the Reds were in good position to outslug Texas -- until the top of the fifth.
The rally began when Vazquez hit a one-out single. He was the first of six consecutive batters to reach base.
"I felt like I had a firm grasp on the game," Belisle said. "It all started with the 1-2 to Vazquez. It was a back-door breaking ball, and it just wasn't a good pitch."
Belisle caught a break after Kenny Lofton's single when center fielder Josh Hamilton made a spectacular laser throw to the plate that nailed Vazquez for the second out. Although the ball was a little up the third-base line, catcher David Ross caught it on the fly and tagged the runner on the back.
"Josh gave us a chance to get out of it," manager Jerry Narron said.
Frank Catalanotto hit an RBI double, then Michael Young was walked on four pitches to load the bases for Sosa. The slugger had been stuck firmly at two shy of 600 for 17 straight games until Friday.
"That's what cost us the game," Dunn said. "The guy has 599 of them. That's not a fluke. I mean, he's one of the most prolific home run hitters in the game."