Servais said Diaz wouldn't pitch in Saturday night's rematch with the White Sox, then likely would be given at least one more set-up situation before being considered for a return as closer.
"We'll take one more good one and see where we're at," Servais said. "You can see how the bullpen is being managed, we're trying to match up and see who is available. Next time out there, he could be out there in the ninth. Last night, he did pitch in the eighth and ninth. We needed to pitch him and that's what the game called for."
Servais would have used Diaz earlier in Friday's game, but starter Ariel Miranda was strong through seven innings and turned a 1-1 tie over to Diaz in the eighth.
"I feel very confident that if he keeps moving in that direction, he'll be back doing the ninth inning solo and we can get back to him being our anchor," Servais said. "That's what we're trying to get back to."
Diaz has a 4.67 ERA in 17 appearances this year and hasn't had the same command he showed last year as a rookie. He gave up a walk-off homer in the ninth at Toronto on Sunday, then walked four batters while getting just one out on Monday against the A's before being replaced by Zych.
Now, he'll take another quick breather after Friday's 29-pitch outing, which included a pair of strikeouts and a steady stream of 97-98 mph fastballs.
"We'll let him regroup, but I was really encouraged by what we saw," Servais said. "That was one of his better outings of the year, maybe his best. He commanded the fastball to the glove side, he had an idea where it was going. He stepped off the mound a few times and gathered himself and said, 'This is what I've got to do.' He's starting to get those checkpoints down so he can get himself back on track. And I thought his slider was good, too."
Servais was pleased the youngster remained calm even after the White Sox got a pair of runners on in the eighth on a high chopper off the plate and an infield single in the hole at short.
"He hung in there and looked very calm," Servais said. "He worked through it. He was pitching, not just throwing."
Greg Johns has covered the Mariners since 1997, and for MLB.com since 2011. Follow him on Twitter @GregJohnsMLB. This story was not subject to the approval of Major League Baseball or its clubs.