Arenado, a five-time All-Star acquired from Colorado on Feb. 1 after eight seasons with the Rockies, followed a walk to Austin Dean with the score 1-1. Arenado turned on a first pitch 96.6 mph offering from Drew Rasmussen (0-1) and sent the ball 373 feet to left for his second homer this season.
Arenado pointed to the St. Louis dugout just before rounding first and screamed as he helped the Cardinals to their fourth straight win, setting off cheers from a crowd limited by coronavirus protocols to 13,328.
Adam Wainwright started his sixth home opener, tying the franchise record set by the late Bob Gibson. The Cardinals wore patches with No. 45 on their left sleeves in honor of Gibson, the Hall of Famer who died Oct. 2.
Wainwright, a 39-year-old righthander, allowed one run and five hits in five innings with six strikeouts and two walks.
Giovanny Gallegos (2-0) gave the Cardinals their third straight inning of hitless relief, following Ryan Helsley and Andrew Miller.
Alex Reyes finished the six-hitter for his third save, allowing a leadoff single to Omar Narváez in the ninth and stranding him at third when Daniel Robertson hit a game-ending flyout.
Milwaukee’s Corbin Burnes gave up one hit in six scoreless innings, struck out nine and walked none.
Travis Shaw had three hits for Milwaukee.
Keston Hiura doubled leading off the third to break an 0-for-20 slide that started the season and scored when Wainwright’s pickoff attempt sailed into centerfield and Dylan Carlson, who overran the ball on a play scored a double error.
Tyler O’Neill had a tying infield single off Eric Yardley in the seventh.
Milwaukee INF Kolten Wong received a standing ovation leading off the game. Wong spent eight years with the Cardinals before St. Louis declined his option last fall. He became a free agent and signed with the Brewers.
ROLEN TO NOLAN
Former St. Louis third baseman Scott Rolen threw out the ceremonial first pitch to Arenado. Rolen spent 17 seasons in the major leagues, including 2002-2007 with the Cardinals.
Brewers: RHP Justin Topa was been moved to the 60-day IL with elbow discomfort.
Cardinals: INF Paul Goldschmidt was held out of Thursday’s game due to lower back tightness. The team said it was a precautionary measure.
St. Louis RHP Carlos Martinez (0-1, 7.20) will face RHP Adrian Houser (0-1, 3.60) in the second of the three-game series on Saturday. Martinez, who will be making his 125th career start, is 6-5 with a 2.23 ERA in 15 starts against the Brewers. Houser has allowed 11 runs in 17 1/3 innings against St. Louis.