The three-game Conference USA series continues Saturday and Sunday.
UTSA took a 2-0 lead with single runs in the first inning on a sac fly by Antonio Valdez and second inning on an RBI double by Matt King. Western Kentucky tied it at 2-2 with two runs in the top of the fourth.
Diaz broke the tie when his homer cleare d the 405-foot mark on the batter’s eye in center field.
Roadrunners starting pitcher Luke Malone got the win to raise his record to 3-2. He went 7.0 innings and allowed two runs on six hits with eight strikeouts and one walk.
Simon Miller pitched the last two scoreless innings to pick up his third save
UTSA is 21-6 on the season and 6-1 in conference.
