St. Louis Cardinals' Alex Mejia, right, is congratulated by Stephen Piscotty after hitting a solo home run during the eighth inning of the team's baseball game against the Washington Nationals on Saturday, July 1, 2017, in St. Louis. The Cardinals won 2-1. (AP Photo/Jeff Roberson)

ST. LOUIS — Former Arizona Wildcats standout Alex Mejia’s first two major-league hits — including an eighth-inning home run — were the difference as the St. Louis Cardinals defeated the Washington Nationals 2-1 on Saturday night.

The Cardinals have won four straight and six of their last seven.

Washington, which is the only team in the National League yet to be shut out this season, has lost three straight and five of its last seven.

Michael Wacha (5-3), celebrating his 26th birthday, was coming off his best start in more than a month and tossed six scoreless innings. He surrendered four hits, including two to Anthony Rendon, struck out a season-high nine and walked one.

Washington left-hander Gio Gonzalez (7-3), who was coming off a loss to the Cubs, was nearly as good against an all right-handed-hitting Cardinals lineup that included four rookies. He allowed one run and two hits over seven innings, striking out nine and walking two.

Mejia, appearing in his third game since being called up, provided the offense for the Cardinals.

His first hit, an RBI single to center, gave the Cardinals a 1-0 lead in the second inning. In the eighth, the 2012 Pac-12 Player of the Year deposited the first pitch from reliever Sammy Solis into the left field seats for his first home run and a 2-0 lead.

Cardinals manager Mike Matheny switched up his late-inning bullpen options, using Seung Hwan Oh in the eighth and Trevor Rosenthal in the ninth. Oh suffered his third blown save of the season in 19 chances on Tuesday in Arizona.

Rosenthal, who had 48 saves in 2015 and 45 in 2016, lost the closer’s role last season. He struggled Saturday, surrendered an RBI single to Stephen Drew in the ninth and was pulled in favor of Matt Bowman after the Nationals loaded the bases with two outs. Bowman struck out pinch-hitter Adrian Sanchez looking on the ninth pitch of the at-bat for his first career save.

Matheny earned win No. 500 on Saturday, becoming the second-fastest Cardinals manager to reach that number behind Billy Southworth. Matheny is also the second-fastest active manager to reach that mark behind Joe Girardi of the New York Yankees.