Ross has continued to shine since then and will try to extend his career-best win streak to five on Friday night.
Lynn (12-8, 2.97 ERA) is 4-2 with a 2.03 ERA in his last seven starts, and allowed two runs over six innings in San Diego on July 29. In his only start against the Cardinals, Ross (11-10, 2.63) yielded one run in his six innings despite walking five and fanned seven in a 3-1 victory.
Ross is 5-2 with a 1.53 ERA in eight starts since the beginning of July. Only Corey Kluber's 1.33 ERA for Cleveland and Clayton Kershaw's 1.42 for the Los Angeles Dodgers are better among qualifying pitchers.
Ross gave up two runs over six innings Sunday in an 8-2 win at Pittsburgh.
Lynn, meanwhile, yielded three runs and matched a season high by allowing nine hits in 5 2-3 innings that same day in Baltimore. He got enough support to come away with an 8-3 victory, his first in four starts.
Lynn had given up two runs or fewer in six consecutive starts.
"He was great. (His innings) all weren't easy," manager Mike Matheny said. "They were stressful, everyone except one, and he seemed to make it happen. That's the kind of pitcher he's developing into."
Lynn will next try to lead the Cardinals (64-56) to a third straight victory and their sixth in seven home games. St. Louis nearly blew a pair of two-run leads in Thursday's opener but A.J. Pierzynski's tag of Alexi Amarista at the plate in the ninth was upheld by video review in a 4-3 victory.
Jon Jay hit a tiebreaking two-run double in the eighth and ended the Padres' season high-tying five-game win streak.
"Sometimes the calls are going to go your way, other times they aren't," San Diego catcher Yasmani Grandal said. "That's the way the game is."
St. Louis has won six of nine over San Diego (57-63) and 19 of 23 home matchups. The Cardinals lead the NL wild-card race by a half-game over Pittsburgh and a game over San Francisco. The Cardinals are also two games behind Milwaukee in the NL Central.
Lynn will attempt to give his team a lift with another strong showing against the Padres. He was 1-1 with a 5.73 ERA in his two meetings before the loss last month.
Jhonny Peralta will try to do his part while breaking a franchise record. He hit his 16th home run Thursday, putting him in a tie with Daryl Spencer (1960) and Edgar Renteria (2000) for the most in one season by a Cardinals shortstop.
Peralta, batting .226 with one home run in 10 all-time games against San Diego, is 0 for 3 with two walks and one strikeout against Ross in his career. Matt Carpenter is 2 for 2 with a double versus the right-hander.
Yangervis Solarte is hoping to return soon from a strained left oblique that caused him to leave Wednesday's 5-3 win over Colorado. The Padres might be tempted to give him another day off as he's 0 for 6 lifetime against Lynn.