Karros (back) will start at third base and bat fifth in Friday's game versus the Pirates.

Karros was out of commission the previous two days while dealing with back tightness, but he's ready to go for Friday's series opener in Pittsburgh. The rookie infielder is off to a nice start in his first 12 big-league games, slashing .270/.386/.432 with one home run.

House went 3-for-4 with a double, two runs scored and an RBI in Thursday's win over the Mets.

The rookie third baseman is still adjusting to big-league pitching, but he continues to offer occasional glimpses of his upside. House hasn't homered since July 13, and during his 25-game power drought the 22-year-old is slashing just .221/.225/.256 with a 30.3 percent strikeout rate. His minor-league resume offers hope that a turnaround will come eventually, although it might not happen until next season -- after posting a poor .655 OPS in his first taste of Triple-A in 2024, he delivered an .872 OPS in 65 games at the level this year to earn his promotion.

Alvarez will be Atlanta's starting third baseman for the rest of the season after Austin Riley (abdomen) underwent season-ending surgery, Mark Bowman of MLB.com reports.

While manager Brian Snitker suggested that in the long run Alvarez might be better suited to a utility role, the 22-year-old will get a chance to change that impression over the final month-plus of the season. Through 91 plate appearances in the majors this year, Alvarez is slashing .247/.330/.309 with zero homers or steals, but he did hit 10 home runs and steal 10 bags with an .861 OPS over 64 Triple-A contests in 2024.

Bregman went 3-for-5 with a double and a walk in Thursday's 6-3 win over the Yankees.

Bregman wasn't directly involved in any run production, but he still had a strong game from the No. 2 spot in the order. The third baseman went 0-for-7 with three walks over this week's two-game series versus the Orioles but bounced back Thursday. Bregman has hit well overall, batting .303 with a .926 OPS, 16 home runs, 24 doubles, 52 RBI, 49 runs scored and a stolen base through 82 contests this season.

Westburg (ankle) remains out of the lineup for Thursday's game against the Astros, Jacob Calvin Meyer of The Baltimore Sun reports.

He hasn't played since departing Monday's contest versus the Red Sox with right ankle discomfort. Westburg is considered day-to-day, and Orioles interim manager Tony Mansolino expressed optimism Thursday that the third baseman can avoid the 10-day injured list. Jeremiah Jackson is occupying the hot corner and batting second in the series opener Thursday.

Atlanta announced Thursday that Riley (abdomen) underwent season-ending core injury surgery.

Riley is expected to be ready for the start of spring training in February. The third baseman has been out since Aug. 2 and had been experiencing soreness in his abdominal area, and he was rehabbing to play again this year before suffering a setback this week. With surgery now in the rearview mirror, Riley's 2025 season is officially over, and he finished with a .260/.309/.428 slash line, 16 home runs, 54 RBI, 54 runs scored, two stolen bases and a 27:128 BB:K across 447 plate appearances. Now that he's done for the year, Riley will have missed a total of 112 games over the past two seasons.

DeJong will start at second base and bat third in Thursday's game against the Mets.

DeJong will remain in the lineup for a fourth straight game, with the Nationals having faced two lefty starters and two righty starters during that stretch. Despite his recent usage, DeJong is likely to remain limited to a part-time role against right-handed pitching, as the Nationals are expected to continue deploying Luis Garcia at second base, Brady House at third base and CJ Abrams at shortstop for the majority of those matchups.

Dodgers manager Dave Roberts said Thursday that Muncy (oblique) has started taking swings off a tee, Fabian Ardaya of The Athletic reports.

Muncy did not feel any soreness in his right oblique while swinging off a tee, as he continues to move in a positive direction with his recovery. It's not clear what the next step is for the third baseman, but he could be ready to take batting practice soon.

The Red Sox announced that Mayer underwent a successful right wrist arthroscopy Wednesday, Lauren Campbell of MassLive.com reports.

After initially spraining his wrist in late July, Mayer had hoped that a cortisone shot plus extended rest and recovery time would be enough for him to heal up from the injury and return to action before the end of the season, but surgery was ultimately deemed necessary. Mayer has now sustained season-ending injuries in each of the last three years, as his 2023 campaign was cut short by a shoulder injury, and his 2024 season ended prematurely due to lumbar strain. The 22-year-old -- who previously suffered the same wrist injury in 2022 but avoided surgery -- will face a three-month recovery timeline from his procedure, putting him on track to be back to full health ahead of spring training. Mayer will likely need a strong camp to solidify himself as an everyday player for the Red Sox heading into 2026, after he produced a .228/.272/.402 slash line with a 30.1 percent strikeout rate over 136 plate appearances with Boston prior to being shut down with the sprained wrist.

Karros is out of the lineup for Thursday's contest versus the Dodgers.

Karros will miss a second straight start while he deals with back tightness. He's considered day-to-day and will attempt to return to the lineup sometime over the weekend in Pittsburgh. Orlando Arcia will man the hot corner and bat eighth for the Rockies on Thursday.