Left-hander Dillon Overton was optioned to Tacoma to make room for Heston.
Command issues, particularly with his sinker, plagued Heston in his first Major League start since 2015, as the 29-year-old right-hander walked three of the first five batters he faced. Four consecutive singles followed, allowing the White Sox to jump out to a 5-0 lead.
"You definitely don't want to be putting people on with free passes," Heston said. "That was really what bit me, not being able to command the zone. Especially a sinkerball guy like me, that's kind of what I do, is command the zone and get early outs."
Heston encountered a red-hot White Sox lineup, which combined to hit .367, collected four home runs and produced 24 runs in the last two games of the series. Falling behind in counts forced Heston to readjust and throw strikes that were hittable pitches, and the White Sox made him pay with those four consecutive singles in the first, although two came off check-swing dribblers that the infield could not handle.
Servais emphasized the importance for his pitchers, especially those up from the Minors in temporary roles, to stay true to their stuff. Heston said he strayed away from that during Sunday's start.
"I think you go out there and put a little more pressure on yourself than you need to instead of just going out there and doing what got you here," Heston said of pitching directly after being called up.
"Today I kind of fell into that a little bit. I was trying to do more than I needed to do."
Heston became Seattle's 11th starting pitcher used this season, the most in the Majors, as the Mariners currently have five starters on the disabled list. Heston took the spot of Chase De Jong, who made four starts before being sent down to Tacoma earlier this week.
He was 2-1 with a 3.41 ERA in six starts for Tacoma and pitched one game in relief for Seattle earlier this season, allowing five runs on seven hits -- including two home runs -- in two innings on April 25 in the game in which Felix Hernandez hurt his shoulder.
Hernandez, James Paxton, Hisashi Iwakuma, Drew Smyly and fill-in starter Ryan Weber are all sidelined with various injuries, with only Paxton expected back by the end of May.