Matt Shaw was supposed to have his first day off as a big leaguer with the Chicago Cubs.

He showed he was still ready to perform when called upon.

The rookie hit his first major-league home run, a solo shot to left field as a pinch hitter in the seventh inning that extended the Cubs’ lead to 4-1 over the Arizona Diamondbacks. The Cubs would go on to hang on and beat Arizona 4-3 in a chaotic finish, highlighted by a heads-up defensive play by Dansby Swanson.

“I think that’s just kinda [the] aggressiveness from Matt and intent from Matt [and] is something that you can’t lose,” manager Craig Counsell said after the game. “He’s good at it. He can hit home runs and it was just an aggressive swing and it’s the kind of swing you want Matt to take, just those aggressive hacks.”

It’s Shaw’s third career hit. He was on the bench to start Saturday’s contest. The Diamondbacks were starting Brandon Pfaadt, a tough righty, so manager Craig Counsell turned to rookie Gage Workman to start at third base. Workman was making his major-league debut after being selected in the Rule 5 Draft in December.

In the seventh inning, though, the Diamondbacks turned to lefty reliever Jalen Beeks with Workman due to lead off the frame. Counsell brought in Shaw and he needed just one pitch to do damage.

Shaw crushed a 95-mph fastball to the left field bleachers with a 98.9-mph exit velocity.

“It’s really cool for Matty, just to be able to kind of get it off his shoulder in a way,” Swanson told Taylor McGregor after the game. “There’s obviously some pressure that comes with, what he’s being asked to do. There’s nobody better to handle it.

The 2023 first-round pick made the team on Opening Day as the team’s starting third baseman and was touted for his offensive prowess. In 159 career minor league games, Shaw slashed .303/.384/.522 (.906 OPS) with 29 home runs, 99 RBI and 46 stolen bases.