NEW YORK — For just the second time all season, the Red Sox will use an opener Monday night in Baltimore.

In a surprise, Boston announced that lefty reliever Brennan Bernardino will start the club’s series opener against the Orioles. It was thought that the two candidates to make that start were Richard Fitts, who is on the roster, and lefty Kyle Harrison, who is at Triple-A. Harrison didn’t make his scheduled start Sunday in Worcester as the Red Sox considered promoting him for his team debut.

Instead, Bernardino — who has made 10 career starts, including one against the Reds on July 2 — will get the nod as the Red Sox try to maximize matchups against the Orioles, who have good left-handed hitters at the top of their lineup. Fitts, who did not pitch in relief in any of the four games at Yankee Stadium in the series the Sox just completed, fits as the bulk reliever who will follow Bernardino and pitch multiple innings. Fitts warmed up briefly Sunday night but the Red Sox instead used Walker Buehler to cover 2 ⅓ innings to finish the game in a 7-2 loss. Buehler’s demotion to the bullpen is why the Red Sox have Monday open.

Bernardino, who got four outs Sunday on 18 pitches and struck out two batters in relief of Dustin May, will likely only be available for an inning. The lefty, who was recalled to the roster last week after spending the entirety of August at Triple-A, has a 2.93 ERA in 49 games (46 innings) so far this season. He has held lefties to a .186 average.

Using a combination of Bernardino and Fitts allows the Red Sox to proceed without removing anyone from their roster to call up someone like Harrison. The Orioles will start Japanese rookie Tomoyuki Sugano in the opener. The Red Sox will send Lucas Giolito, Brayan Bello and Garrett Crochet to the mound in the final three games of the series at Camden Yards.