Latos (6-1) hadn't lost a regular-season game since last August, setting a club-record streak of avoiding defeat. He couldn't overcome Pittsburgh's three-run first inning.
Charlie Morton (1-1) was better during his second start since returning from elbow surgery. He gave up three singles and threw 61 pitches in 5 1-3 innings, starting the Pirates toward their NL-leading 12th shutout.
Latos had nine of Cincinnati's 17 strikeouts, which matched the club's nine-inning record. The Reds also had 17 strikeouts on opening day, but that came in a 13-inning loss against the Los Angeles Angels.
Cincinnati's lineup managed four hits while getting shut out for the second time in their last four games.
GIANTS 5, PADRES 4
SAN FRANCISCO (AP) — Juan Perez hit a tiebreaking single with two outs in the eighth inning and San Francisco snapped San Diego's seven-game winning streak.
Perez's clutch swing came after pinch hitter Jesus Guzman gave San Diego a 4-3 lead with a two-run homer in the top half of the inning
Brandon Belt finished with three hits to help the Giants move into a second-place tie with Colorado in the NL West.
Jean Machi (2-0) retired one batter for the win and Sergio Romo worked the ninth for his 17th save. Dale Thayer (0-3) took the loss.
San Francisco ace Matt Cain and Andrew Cashner each had a strong start. Cain had a season-high 10 strikeouts in seven innings and was charged with two runs. Cashner scattered 10 hits over 6 2-3 innings and allowed three runs.
PHILLIES 4, NATIONALS 2
PHILADELPHIA (AP) — Cliff Lee struck out nine in eight impressive innings for Philadelphia, and Michael Young tied a career high with three doubles.
Lee (9-2) allowed two runs and five hits to win his fifth straight decision. The three-time All-Star left-hander lowered his ERA to 2.53 and helped the Phillies move into a second-place tie with the defending NL East champion Nationals.