Mitch Keller is the Pirates' top pitching prospect. He has yet to show it, though. Pressed into service due to the Pirates' multiple pitching injuries, Keller is struggling to solve big league hitters with an 8.29 ERA and 1.87 WHIP. He has a 10.97 ERA in his past three outings. 
Keller has given up at least one homer in four of his last five starts. The Mariners rank ninth in homers and expect to activate power-hitting outfielder Domingo Santana from the injured list in time for this game. Santana is second on the Mariners in RBI's. 
I'm not buying Keller as a favorite in this matchup of two bad teams. The Mariners are throwing their No. 1 pitcher, lefty Marco Gonzalez. If you discount his recent starts against the powerful Astros, Gonzaez has surrendered three or fewer runs in seven of his last eight starts. He was solid in his past start, a 5-3 home victory against the Reds this past Wednesday. Gonzalez held Cincinnati to two runs on five hits in seven innings. 
Pittsburgh is 14-25 versus lefty starters this season. 
Seattle is 4-2 in its last six games. The Pirates are home for the first time in nine days. They just were swept three games by the Cubs getting outscored by 32 runs in that series. Pittsburgh has dropped 19 of its last 27 home games.