The defending World Series champions trailed 6-1 after the fourth inning of the interleague matchup, with starter Clay Buchholz walking a career-high eight in only three-plus innings.
But Ortiz tied it by hitting a three-run homer off Ervin Santana in the fifth. With Red Sox fans at Turner Field chanting ''Papi! Papi!'' the World Series MVP then gave Boston the lead with a bases-loaded sacrifice fly off Ian Thomas (1-2) in the seventh.
Following pregame declarations of confidence from manager John Farrell and general manager Ben Cherington, the Red Sox came back to end their worst skid since an 11-game slide in 1994.
Jansen also worked the ninth, retiring Devin Mesoraco with two on for his 15th save.
Ryu (5-2) was charged with three runs and three hits in 7 1-3 innings, improving to 6-0 in six starts against the Reds. He struck out seven and walked none while winning for the first time at Dodger Stadium this season.
Johnny Cueto (4-4) allowed four hits and four runs - one earned - in 6 1-3 innings.
ST. LOUIS (AP) - Brian Roberts hit a tiebreaking single in a three-run 12th inning after Brett Gardner's leaping catch at the left-field fence kept New York alive in the 11th.
Pinch-hitter Alfonso Soriano and Brendan Ryan each added an RBI for the Yankees, who took the opener of a three-game interleague series for their third straight win. Alfredo Aceves (1-2) worked two scoreless innings and David Robertson earned his 11th save in 12 chances.
Jon Jay had an RBI double in the 12th for the Cardinals, who lost for the third time in 12 games.
A standing-room crowd of 47,311, the third-largest at 9-year-old Busch Stadium, showed up to see an opponent making only its second appearance in St. Louis since losing to the Cardinals in the 1964 World Series.
Cardinals pitchers retired 20 of 21 batters before the 12th, when Randy Choate (0-2) faced five batters and four reached safely.
NEW YORK (AP) - Gaby Sanchez tagged the Mets again, hitting a tiebreaking single in the ninth inning and a pinch-hit homer in the eighth that sparked Pittsburgh's come-from-behind victory.
The Mets announced after the game that they had fired hitting coach Dave Hudgens. They also cut reliever Jose Valverde, who gave up Sanchez's go-ahead hit.
Sanchez upped his average against the Mets to .324 and has 34 RBIs against New York, his best totals against any NL team. He homered off Scott Rice while hitting for Ike Davis, who was making his return to Citi Field after being traded to the Pirates in mid-April.
Valverde (1-1) was booed off the field after allowing pinch-hitter Jose Tabata's tying single in the eighth. Valverde returned for the ninth and was even worse.
A day after Dodgers right-hander Josh Beckett threw a no-hitter against the Phillies, leadoff man Ben Revere started with a single for the first of Philadelphia's 12 hits.
Kendrick (1-5) allowed six hits over 6 2-3 innings to earn his first win since last Aug. 6, a span of 16 winless starts. His best performance in a while came against the top offense in the majors. The Rockies are first in runs (262) and batting average (.291).
Jhoulys Chacin (0-4) gave up four runs and seven hits in five-plus innings. He has lost five straight decisions dating to last season.