The right-hander will try to build on his impressive debut while leading the visiting Red Sox to consecutive wins for the first time in three weeks Tuesday night against the Cincinnati Reds.
Kelly (0-0, 1.29 ERA) averaged five innings in his seven starts for the Cardinals before being shipped with Allen Craig to Boston (52-65) on July 31 for John Lackey.
It was a different story in an emotional Red Sox debut for Kelly on Wednesday. Making his return to Busch Stadium, he allowed one run and three hits over seven innings of a 2-1 win.
Kelly didn't get the decision as the Red Sox pushed across the go-ahead run in the top of the ninth.
"The only thing I want to do is just win," he told MLB's official website. "That's what I do every single game."
Kelly will try to lead Boston to its first back-to-back victories since a five-game winning streak July 13-21 as the club opens a two-game series at Great American Ball Park.
In his only start against the Reds, Kelly gave up one run over six innings of St. Louis' 6-1 home victory Aug. 27.
Cincinnati slugger Todd Frazier, 3 for 5 against Kelly, hasn't homered in his last 20 games.
Devin Mesoraco tied Frazier for the team lead with 20 home runs - the most in baseball among catchers - by hitting a grand slam and a two-run shot Sunday as the Reds avoided getting swept with a 7-2 home win over Miami.
Cincinnati (60-58) looks to bounce back with its eighth win in 12 games as it turns to Mat Latos (4-3, 3.12).
The right-hander seeks his third consecutive victory after allowing three runs over 7 2-3 innings of an 8-3 home win over Cleveland on Wednesday. He tossed seven scoreless innings before allowing three runs in the eighth.
Latos, who missed the first 2 1/2 months of the season due to elbow, knee and calf injuries, showed better command with two walks after he had issued eight over his previous two outings.
"A lot of what helped was a lot of strike ones for me," he said. "(I tried to) pound the zone down and keep it down, and getting strike one and going from there."
Latos hasn't been as sharp at home with a 4.45 ERA in five starts compared to a 1.85 mark in five on the road.
He gave up four runs and 10 hits over 5 2-3 innings of a 5-4 win for San Diego at Fenway Park on June 21, 2011, in his only career start against the Red Sox. Latos didn't get the decision.
Boston's Dustin Pedroia is 1 for 1 with three walks against Latos. The four-time All-Star is batting .367 over his last 11 games after going 2 for 4 in Sunday's 3-1 road win over the Los Angeles Angels.
Recent addition Yoenis Cespedes has recorded at least a hit in all six games on the current eight-game trip after hitting his 18th homer Sunday.
The Red Sox have won seven of eight meetings with the Reds, sweeping a two-game set at Fenway in May.