Lynn, an 18-game winner last season, picked up a no-decision in his opening start after allowing four runs on six hits in four innings of the Cardinals' 10-9 loss in Arizona.
He bounced back for a victory in his next outing six days later, holding the Cincinnati Reds to a single run in six innings with 10 strikeouts in a 5-1 victory on April 9.
He's 2-1 with a blown save and a hold in six career meetings with Pittsburgh - including four starts - while allowing the Pirates to compile 22 hits and 14 runs in 26 1/3 innings. Lynn is 1-0 in three career trips to PNC Park with a 1.74 earned run average across 10 1/3 innings.
Pittsburgh replies with right-hander James McDonald, who can continue a career's worth of success against the Cardinals.
The 28-year-old Californian is 4-1 in 10 meetings with St. Louis with a 2.27 ERA in 39 2/3 innings, including two wins in two starts last season while allowing just four hits in 13 scoreless innings.
He's 15-6 in 40 career outings at PNC Park.
McDonald allowed a run and two hits in seven innings of a tough luck loss to the Chicago Cubs in his 2013 debut on April 4, then allowed four runs in five innings of a 6-5 win at Arizona on April 9.
On Sunday in St. Louis, the Cardinals' scoreless streak came undone in the late innings as the Milwaukee Brewers lit up the bullpen and escaped Busch Stadium with a 4-3 win on Jonathan Lucroy's home run in the 10th inning.
Lucroy cranked a solo homer deep to left-center off Fernando Salas (0-2) to seal Milwaukee's comeback after Ryan Braun ended a string of 39 consecutive scoreless frames by the Cardinals' pitching staff with a two-run blast in the eighth.
Yuniesky Betancourt sent the game to extras with an RBI double off Mitchell Boggs in the ninth, and three relievers closed out the win in the 10th to end Milwaukee's three-game slide.
Matt Adams went 2-for-4 with a solo homer for St. Louis, which had won four straight and stranded the tying run on second in the 10th.
Cardinals starter Jaime Garcia took a no-decision despite scattering seven hits and two walks over seven scoreless innings. His counterpart, Marco Estrada, gave up three runs on seven hits over six frames.
Meanwhile, in Pittsburgh, Starling Marte's eighth-inning home run helped cap the Pirates' comeback and their first three-game home sweep of the Cincinnati Reds since 2010 with a 10-7 victory.
"(The Reds) were one of the premium teams in major league baseball last year," said Pirates manager Clint Hurdle. "To finish the series off, very gratifying, good feeling."
Michael McKenry hit his first two home runs of the season for Pittsburgh, which scored six times in the bottom of the eighth to rally from an early 5-0 deficit and improve to .500 for the first time this year.
Neil Walker went 3-for-5, while Andrew McCutchen and Travis Snider each added two hits and an RBI.
Jared Hughes (1-0) picked up the win for the Pirates despite allowing a run and three hits in the top of the decisive eighth inning. Phil Irwin started for Pittsburgh and allowed five runs - four earned - while striking out four in 4 2/3 innings of work in his major league debut.
The Pirates won eight of 15 games between the teams in 2012, a year after the Cardinals had won the season series, 9-7.
