Cardinals' Riley O'Brien Fits Best With These 2 Contenders

Riley O'Brien could be on the market.

Jun 22, 2026; St. Louis, Missouri, USA; St. Louis Cardinals pitcher Riley O'Brien (61) pitches against the Arizona Diamondbacks during the ninth inning at Busch Stadium. Mandatory Credit: Jeff Curry-Imagn Images | IMAGN IMAGES via Reuters Connect

The St. Louis Cardinals limped into the All-Star break, having lost six of their last 10 games. Though they are only one game back in the wild card race, all signs are pointing to them being sellers.

One of the biggest moves they could make would be to trade All-Star closer Riley O'Brien. He is one behind Mason Miller for the most saves in the National League and still has a few years of club control remaining after 2026. He can also touch 100 mph with his fastball.

If he is to be traded, these two contenders make the most sense for him.

Seattle Mariners

Seattle Mariners relief pitcher Andres Munoz (75) delivers a pitch in the ninth inning of the MLB baseball game between the Cincinnati Reds and the Seattle Mariners at Great American Ball Park in Cincinnati on Wednesday, Sept. 6, 2023. | USA TODAY Network via Reuters Connect

The Cardinals have already made one trade with the Seattle Mariners, sending Brendan Donovan their way back in February. Seattle could afford to give up some young starting pitching that could strengthen the future for St. Louis.

It's also worth remembering that the Cardinals actually acquired O'Brien from Seattle the day after the 2023 World Series concluded, so he would be going back to a familiar place if a deal happens.

The Mariners are a little thin in their bullpen, so adding a lockdown closer or any late-inning arm to pair with Andres Munoz could make a huge difference. If Seattle is willing to meet a high asking price, they could be an easy trade partner for the Cardinals.

Philadelphia Phillies

Jul 9, 2026; Cincinnati, Ohio, USA; Philadelphia Phillies relief pitcher Jhoan Duran (59) pitches against the Cincinnati Reds in the ninth inning at Great American Ball Park. Mandatory Credit: Katie Stratman-Imagn Images | IMAGN IMAGES via Reuters Connect

Yes, the Phillies have Jhoan Duran at the back end of their bullpen, who is near the top of the National League in saves. But O'Brien could fit well there too. Having too such arms could give the Phillies a big advantage as they look towards trying to return to the postseason.

They also have some solid prospects in their system that the Cardinals might want, so connecting with Philadelphia might not be a bad idea for St. Louis. The Phillies have overcome a dreadful start to the season, while St. Louis appears to be coming back down to earth.

This could be a good way for the Cardinals to set themselves up well for the future and also capitalize on one of their best assets. Relievers can be volatile, so expecting O'Brien to repeat his dominance next season might be unrealistic.

That's why trading him to a contender would make a lot of sense. It will be interesting to see if Philadelphia is among the contenders they engage in talks with for their closer.