Perez, 30, signed with the Mariners prior to Spring Training as a non-roster invitee and was not on the 40-man roster. To make room for the reliever, Seattle designated Minor League outfielder Chih-Hsien Chiang for assignment.
"[Perez] was throwing the ball well in Triple-A, obviously a lot of big league experience -- different role for him out of the bullpen -- high strikeout ratio from the left side, so we felt like it was a good time to take a look at [him]," Mariners manager Eric Wedge said.
Perez posted career bests in back-to-back seasons for the Mets in 2007-2008 as a starter. He won 15 games in 2007 and then 10 in 2008, when he struck out a career-high 180 in 194 innings, also a career best. Since then, the lefty has struggled through patellar tendinitis and has transitioned to the bullpen. He has not pitched in the Major Leagues since 2010, although he played in the Nationals organization last season.
"After I got the call -- yesterday, I think -- I felt very excited because my last three years I was not that great and it was really tough for me," Perez said. "I almost retired because it's not easy, it's not easy being in this situation."
After pitching with the Nationals' Double-A club last season, the coaches told him he could evolve into a lefty specialist out of the bullpen if he put in the work. That spurred him to play winter ball this past offseason, and he said his velocity is now up.
In 22 games with Tacoma this year, Perez was 2-2 with a 4.65 ERA and one save out of the bullpen. He had 42 strikeouts and 19 walks in 31 innings pitched. He said he normally would throw more than one inning per outing with Tacoma.
Delabar, 28, opened the season with the Mariners and posted a 1-1 record with a 5.18 ERA in what was a team-high 25 appearances, but struggled to keep the ball in the park, allowing seven home runs. He was optioned to Tacoma on May 30 but was recalled June 13. Delabar pitched two scoreless innings on June 14 in his only appearance since rejoining the Mariners.
Chiang, 24, has spent time with Tacoma and most recently Double-A Jacksonville this season. He originally came to the Mariners from the Red Sox as part of the Erik Bedard trade in 2011.