Nick Kurtz will start at first base for the AL after Vladimir Guerrero Jr. opts out

The American League All-Star starting lineup at first base just changed, with Oakland’s Nick Kurtz moving into the spot originally held by Toronto’s Vladimir Guerrero Jr. Guerrero had been voted in as a starter, but opted out shortly after the rosters were set, prompting the league to turn to the next available choice for the starting role.

According to Yahoo Sports, Kurtz was elevated to the starting position after Guerrero told reporters he needs to prioritize treatment and recovery for what’s described as a lower back problem. That means Kurtz, a 23-year-old first baseman for the Athletics, will now make what could be the first of multiple All-Star appearances rather than watching from the bench as a non-starter.

The rise that led to Kurtz’s All-Star start has been unusually fast. Yahoo Sports reported that Kurtz debuted on April 23, 2025, and that his impact in his rookie season came late enough that he did not earn an All-Star nod then. This year, the Athletics’ first baseman has taken a more central role in a lineup where his power has shown up in a big way, with Yahoo Sports listing 20 home runs and a.939 OPS for Oakland as the All-Star selection process approached.

Kurtz is the kind of player whose breakout is hard to separate from the team’s current baseball identity. Yahoo Sports also noted the Athletics are in their second of three seasons playing in West Sacramento, before moving to Las Vegas, and that the All-Star start represents a notable spotlight for the franchise during its run in the Yolo County area.

Guerrero’s decision adds another layer to the night for Toronto, since he was not only a fan-voted starter but also one of the game’s marquee names at the position. SRN News, citing Sportsnet, reported that Guerrero has dealt with periodic back issues, missed consecutive games against the New York Yankees in mid-June when the ailment flared, and also sat out a game earlier in the week against the New York Mets due to the same problem. SRN News also described his season production as 35 RBIs and four home runs through 82 games.

What to watch next is how the All-Star Game replacement unfolds for both teams. For Kurtz and the Athletics, the immediate focus is on whether his breakout form translates cleanly to a star-studded environment and whether his starting spot becomes a springboard to a wider national profile. For Toronto, the key storyline is whether Guerrero can protect the second half, since opting out with a back issue suggests management is trying to keep the problem from lingering into games that matter most for standings.

For baseball fans, the lineup shift may be minor on paper, but it carries weight in the All-Star context. Star starters are a premium part of the Midsummer Classic, and a late change reshapes matchups at first base while also changing how pitchers and managers plan around a player who, until this week, had been arriving in All-Star conversation rather than prepared to start one. But the reason for the change, as described in the reporting, is not tactical. It is health and recovery.