Guaipe has a 1.42 ERA over his last 15 appearances with the Rainiers. He was in uniform for the Mariners' game against the Rockies on Tuesday night at Coors Field.
"I thought he did a nice job while he was up here before," manager Lloyd McClendon said. "He elevated some balls at one point, but I think he learned from that. I think he's got big-league stuff and I think he's going to be around for a long time."
Ramirez, a right-handed reliever, had yet to pitch for the Mariners after being acquired from the Yankees in the Dustin Ackley trade last Thursday along with outfielder Ramon Flores. Flores has hit .438 (7-for-16) in his first four games with Tacoma.
McClendon said the decision was made to send Ramirez down because he hadn't pitched since last Wednesday, the day before the trade.
"The kid hadn't thrown in five or six days," McClendon said. "It's probably not fair to put him in a ballgame. Guiape is sharp and he's been ready, so we just switched them out. It just made more sense. He's been throwing the ball well."
Ramirez, 25, made three relief appearances for the Yankees earlier this season, but he has pitched most of the year for Triple-A Scranton/Wilkes-Barre, posting a 2.90 ERA with 10 saves in 32 outings.
Seattle's starters have pitched deep into games for the most part since Ramirez's arrival, with Taijuan Walker throwing a complete game and Hisashi Iwakuma throwing 8 2/3 innings, so Ramirez wasn't getting any activity.
"I was trying to get him up and keep him as sharp as we possibly could because he hadn't been in a game for so long," McClendon said. "But you just can't continue to do that. He needs to go down and pitch and throw well and maybe he'll be back here at some point."
• Rookie Ketel Marte wasn't in the lineup Tuesday for the first time since the Mariners' No. 2 prospect, according to MLB.com, was called up from Tacoma last Friday, but McClendon said the 21-year-old will start at shortstop in Wednesday's series finale against the Rockies. He's previously started three games at second base and one in center field.
• If the Mariners need a backup third baseman for Kyle Seager, McClendon said shortstop Brad Miller would likely get the call, with Marte then taking the shortstop duties.
• The Mariners will go with Iwakuma against the Rangers on Friday to open their homestand at Safeco Field, with Mike Montgomery pitching on Saturday and Felix Hernandez on Sunday. That flip-flops Iwakuma and Montgomery from their prior starts, leaving Iwakuma on normal four days' rest with the Thursday off-day, with Montgomery getting an extra day.
McClendon said the switch provides better matchups down the line and also helps with monitoring Montgomery's work load as both he and Walker will have to be watched closely down the stretch as their innings mount.
• With Monday's 8-7 win, the Mariners snapped a 28-game losing streak -- dating back to 1997 -- in nine-inning games where they allowed 18 or more hits. The Rockies lost despite racking up 18 hits. The Mariners are 3-78 in franchise history in games allowing 18-plus hits in nine innings.