Diaz and the Mariners documented the moment on Tuesday after the All-Star recorded the save on Aug. 25 against the Arizona Cardinals.
Servais made the pact with Diaz in July. Diaz sports a haircut with wavy lines on the sides of his head. Diaz had his personal barber come out and give Servais the same custom cut.
"He handled it pretty good," Diaz told MLB.com. "He looks like the best-swaggered manager in the league right now."
Servais got Diaz a custom hat for the job, reading: "Electric Eddie's Barber Shop." He told reporters that he also made a comment to Kyle Seager about another bet, saying he would match his haircut if Seager went 4-for-4 with two home runs. Servais later said that he would not longer do "stupid bets."
The Mariners take on the San Diego Padres at 3:40 p.m. on Wednesday at Petco Park in San Diego.
Diaz leads Major League Baseball in saves and games finished (57). The 2018 All-Star also owns a 1.97 ERA in 64 appearances this season.