Giants add left-hander Seth Lonsway for Saturday doubleheader, shuffle rotation spot

The San Francisco Giants activated a new left-handed option for Saturday’s doubleheader, selecting the contract of pitcher Seth Lonsway and adjusting their pitching assignments around the twin bill against the Arizona Diamondbacks. The moves also included a call-up that determines who starts the first game and a corresponding optioning move to keep the roster in balance.

According to the Giants transaction report published ahead of the day’s games, Matt Wilkinson was called up from Triple-A Sacramento to start Game 1. The team also listed Wilkinson as the official 27th man for the doubleheader, a designation that typically aligns with MLB’s expanded roster rules for teams playing multiple games in one day. For the Giants, that makes Wilkinson the clear choice to open the series, at least in terms of the game-day plan.

To make room for the additional active-roster selection, San Francisco optioned right-hander Spencer Bivens back to Sacramento. The same transaction set paired that optioning with the contract selection of Lonsway, meaning the Giants did not need further roster moves to carry both decisions on the day’s roster. Bivens’ optioning also indicates that the Giants intended to use their bullpen and remaining starters to cover both games without adding another roster spot beyond Lonsway’s selection.

Lonsway, the left-hander the Giants selected, is described in the transaction report as approaching his major league debut. While the day’s moves do not specify what role he will take beyond being on the active roster, contract selection is the key step that puts a player in position to appear for the Giants in the games that follow. In practical terms for fans, it means the Giants are not only altering their pitching staff for the immediate doubleheader, but also giving themselves a fresh look at a new arm during a slate where bullpen usage can be especially consequential.

The doubleheader context raises the stakes of every pitching decision, even when no performance details are known. With two games to manage, the choice to name a specific opener and to add a new bullpen arm can affect how long relievers work and how quickly the team can turn over pitchers between games. Wilkinson’s assignment to start Game 1 also shapes the order in which the Giants can deploy their remaining arms after his outing, while Lonsway’s selection offers another possible bridge in high-leverage moments.

For the Giants, these moves are the kind that often come together when a team needs both immediate game coverage and a longer-term evaluation window. If Lonsway is nearing his debut as reported, this roster addition can be an early indicator of how San Francisco views him as the season progresses. Next, the key questions for Saturday are which of the selected pitchers work in which game, how the Giants manage reliever workload across both contests, and whether the organization keeps Lonsway on the roster in the aftermath of the twin bill.

The transactions reported here come from MLB Trade Rumors and reflect the Giants’ pre-doubleheader roster status as described in that report. Without an additional primary league or team press release in the available material, readers should treat the details as transaction-confirmation level only, and wait for official game-day lineups to confirm roles such as inning usage and who appears in which game.