To make room on the 40-man roster for Rodriguez and Kontos, Pittsburgh designated outfielder Danny Ortiz and reliever Jhan Marinez for assignment. Kontos is effectively replacing Marinez in the Bucs' bullpen.
Claimed off waivers from the Brewers on May 19, Marinez pitched well in a low-leverage role for the Pirates. The right-hander recorded a 3.18 ERA and 1.35 WHIP in 34 innings over 24 appearances.
Kontos, 32, has posted a 3.83 ERA and 1.34 WHIP in 50 appearances for the Giants this season. He owns a 3.05 ERA in 300 games for San Francisco.
"I'm very happy to have him. It's an experienced, Major League reliever that pitched for a very good ball club and pitched in some very meaningful games the past five years," Pirates manager Clint Hurdle said. "We know he's hard to hit. We know the competitor from the other side of the field. I think it was a very, very solid addition."
Kontos, who joined the Giants five years ago in a trade for current Pirates catcher Chris Stewart, was claimed off revocable waivers and let go for no compensation. The Pirates will have to make a pair of corresponding moves before adding Rodriguez (Sunday) and Kontos (Monday) to their active roster.
"We're looking forward to plugging him into our bullpen," general manager Neal Huntington said. "Jhan Marinez did a nice job with us. Got some outs, but was more in a lower-leverage role, and while we liked the stuff and liked the arm, we felt that George Kontos comes in and can pitch in a little bit higher-leverage role for us."
After a mostly quiet non-waiver Trade Deadline, Huntington said the Pirates would actively pursue upgrades during the August waiver trade period. This season, they gained flexibility to add players; they have not paid restricted infielder Jung Ho Kang's $2.75 million salary, did not pay part of Starling Marte's $5 million salary while he was suspended and saved about $2 million by releasing reliever Jared Hughes at the end of Spring Training.
The Pirates used some of that savings Saturday. Rodriguez is set to earn about $7.5 million before his contract expires next season, while Kontos is arbitration-eligible for 2018 and '19.
"The intent was to add quality players to this club to help the 2017 club, but in both cases they have the opportunity to help next year's club as well," Huntington said. "That was the focus, just adding a couple players to help us this year and next."