The Rays' No. 10 prospect struck out eight and allowed three hits over seven innings as Class A Bowling Green blanked Great Lakes, 5-0.
Markel (7-5) retired his first six batters before Jesse Bosnik singled to open the third inning. He followed that up by setting down the next eight, with Bosnik reaching on a wild third strike with two outs in the fifth.
"I just got in a good rhythm. Getting ahead of hitters was the key," said Markel, who faced four batters over the minimum. "I kept pounding the zone and just trying to get the count in my favor.
"Probably my most dominant off-speed pitch tonight was my changeup; I was using it against lefties and righties. The first few times through the order, I didn't really use the slider."
Markel has won five straight decisions and has not allowed a runner to reach third base in his last 15 1/3 innings. After missing a month earlier this year due to an injury, he's went 5-0 with a 2.55 ERA in starts in July.
"Everything is clicking," the 21-year-old right-hander said. "My arm and mind are on the same page. People remember how you finish and I want to finish strong. I feel like I'm back to how I was feeling in the New York-Penn League last year."
A 39th-round pick in the 2010 Draft, Markel went 3-4 with a 3.14 ERA in 13 starts for short-season Hudson Valley last summer.
"I'm learning a lot about pitching, about keeping the pace up, not letting the little things bother you and pounding the zone," he said. "When the pitch is let go, you have to realize there is nothing you can do about it."
Markel was on the bench in the opening inning when teammate Ryan Brett stole home after Drew Vettleson walked.
"The guy on first [Jake Hager] took off, the catcher [Pratt Maynard] thought it was ball three and threw down to second and Brett took off and caught them off-guard," Markel said. "Really fun to watch, really exciting."
Less fun was what happened next as Cameron Seitzer hit a line drive to shortstop that Darnell Sweeney turned into a triple play, the fourth in team history.
"Those are two kind of different plays, but it's baseball and it'll happen," Markel said. "Our offense came out and put guys on base, but there's nothing you can do. It was a hard-hit ball right at someone."
Charlie Cononie fanned three and allowed one hit over the final two innings, finishing off Bowling Green's 10th shutout of the season.
Brett scored twice and Rays No. 11 prospect Josh Sale singled home a run for the Hot Rods, who've won 17 of their last 23 games.