Through the first five games of the season, the St. Louis rotation -- Wainwright, Looper, Thompson, Kyle Lohse and Todd Wellmeyer -- is 4-0 with a 1.17 ERA and has combined for 22 strikeouts and 11 walks in 30 2/3 innings.
"You really have to give credit to the starting pitching," center fielder Rick Ankiel said. "They've just been so solid every day out and hopefully they can continue."
The Cardinals (4-1) close out the three-game series with the Nationals (3-3) at 2:15 p.m. CT on Sunday before heading on the road for six games.
The Cards gave Wainwright (1-0) -- who struck out four, walked one and threw 64 of his 107 pitches for strikes -- some early run support.
St. Louis scored first with back-to-back two-out singles by Wainwright and Cesar Izturis, the No. 8 and No. 9 hitters, in the second inning off Nationals starter Matt Chico (0-1).
Yadier Molina added to the lead with a two-out, two-run single past Nationals first baseman Nick Johnson in the third to score Ankiel and Albert Pujols.
Johnson got the Nationals on the scoreboard with a fourth-inning single to drive in Ryan Zimmerman.
Kennedy made one of the early plays of the season as the next batter, Austin Kearns, hit a ground ball up the middle. Kennedy ranged to his right, made a diving stop and flip to second for a force out.
"Sometimes you have to sit back and applaud," Wainwright said. "That was full-extension, Superman dive, snowcone, turn around and flip it to second. I haven't seen too many plays made behind me like that before."
"Adam Kennedy's play up the middle was just sick," Ankiel said.
After that out, the second of the inning, the Nationals loaded the bases with a single from Ronnie Belliard and a walk to Felipe Lopez before Wainwright retired Jesus Flores on a groundout to third base.
"Who knows where that inning goes if he doesn't make that play?" Wainwright said. "That was a huge, huge play. That was potentially a rally there and he shut it down. It was a big play."
Johnson added a solo home run, his first of the season, in the eighth. He went 3-for-4 with two RBIs. Johnson and Zimmermann (two doubles) accounted for five of the eight hits off Wainwright.
The Cardinals added an insurance run in the eighth when Kennedy scored on a passed ball with two outs. That run turned out to be the difference.
Right-hander Anthony Reyes relieved Wainwright and allowed a two-run home run to Flores in the ninth to cut St. Louis' lead to 5-4. Left-hander Randy Flores came in to record the final out for his fourth career save.