Sonny Guadarrama lofted the ball into the box, where Klèber headed it up and smashed it off the volley past a diving San Antonio FC keeper to give Austin Bold FC an early lead on Thursday night.
It was a stunning start to a dominant game for the Bold, which beat their Texas rivals 4-2 in the third round of the U.S. Open Cup and will travel to face off with the Houston Dynamo in the fourth round on June 11 or 12.
"He did more of the work, mine was the easy part," Guadarrama said.
San Antonio FC scored in the waning moments of both halves. Wálter Restrepo scored with a close-range shot in the 44th minute to cut the Austin lead to a pair of goals at the break, and Jack Barmby scored four minutes into extra time.
Guadarrama finished with one goal and two assists in the game, while forward Andre Lima finished with a brace and Klèber started things off with the game's opening goal.
"Sonny is becoming the Sonny from the past after two years off," Bold head coach Marcelo Serrano said. "He's playing for the community that he loves. That's the reason we brought him back. Every game, he's increasing his level and he's getting the fitness back again. He's a baller."
After losing two straight games for the first time all season, Austin experimented with a 4-3-3 formation for the first time, with Guadarrama in the middle and Lima, Klèber and Isaac Promise up top.
It worked, as the Bold outshot San Antonio 26-16 - including a 9-6 advantage in shots on target - and had 52 percent of the possession.
"We're disappointed with the outcome of the game," San Antonio FC head coach Darren Powell said. "We were able to play some young players who earned valuable experience and now know what it's like to play at this level. It was a very open game with plenty of chances both ways, but the bottom line is we need to regroup and prepare for our league game on Saturday."
The Bold locker room is filled with former MLS players and players with Open Cup experience.
Defenders Amobi Okugo and Jermaine Taylor each spent a few seasons in the top professional league, and Okugo was a member of Sporting Kansas City when they won the Open Cup in 2015.
Diego Restrepo was the starting goalkeeper for the Fort Lauderdale Strikers that made it to the quarterfinals of the tournament in 2016, upsetting MLS teams D.C. United and Orlando City SC along the way.
The Open Cup is something that Austin has made a high priority in its first-ever season.
"We knew what was at stake," Guadarrama said. "When we started back in February, one of our bigger goals was to be on a bigger (stage) and we knew for that to happen we have to play against an MLS team."