SAN FRANCISCO — Giants right-hander Johnny Cueto departed Wednesday’s series finale against the Reds in the top of the sixth inning at Oracle Park due to lat tightness.

Cueto blew a 93.5-mph fastball past Nick Castellanos for his fourth strikeout of the afternoon, but he appeared to grimace after throwing the pitch and immediately signaled to catcher Curt Casali that he was done. Head athletic trainer Dave Groeschner quickly came out to check on Cueto, who subsequently walked off the field after working 5 2/3 scoreless innings on only 68 pitches.

Cueto’s exit is a worrisome development for the starting rotation. The 35-year-old veteran dominated in his first three starts of the year, logging a 1.80 ERA over 20 innings.

Cueto allowed only three hits against the Reds, his former club, on Wednesday and departed with a 2-0 lead. Left-hander Caleb Baragar replaced Cueto in the sixth and induced a groundout from Joey Votto to end the inning.