News of Pham's addition came shortly after Boston agreed to send longtime catcher Christian Vazquez to the Houston Astros. But Boston moved quickly to replace Vazquez, acquiring catcher Reese McGuire and a player to be named later or cash from the Chicago White Sox for left-handed reliever Jake Diekman, the team announced.
Whether the Red Sox would be trading for short-term help or looking to the future before Tuesday's trade deadline had been one of the bigger question marks in baseball. Boston has struggled since the All-Star break, dropping to 52-52 and into last place in the American League East. However, it's just 3 games behind the final AL wild-card spot.
Pham, 34, was hitting .238 with 11 home runs and 57 runs scored in his first season in Cincinnati -- one in which he drew national headlines for a fantasy football dispute that turned physical in May with Joc Pederson of the Giants. Pham has a $1.5 million mutual option in his contract for the 2023 season.
"Tommy's a really good major league player," Boston general manager Chaim Bloom said. "He's a good hitter. He manages an at-bat really well. And that's something that I think will be a huge benefit to our group. He hits the ball hard. He knows the strike zone. He is a competitor. He's a really knowledgeable hitter. Understands himself. Very passionate about hitting. Just a guy that has a lot of talent and has proven that over the course of time at the major league level."
McGuire, 27, has a .225 average in 53 games. He's eligible for arbitration the next three seasons. A first-round pick of the Pirates in 2013, he has thrown out 11 of 36 attempted base stealers this season, a 30.6% mark that ranks fourth best in the American League.
McGuire became expendable for the White Sox when Yasmani Grandal returned after being sidelined by lower back spasms. McGuire also was outplayed by catcher Seby Zavala, who was batting .296 with two homers in 30 games heading into Monday night's series opener against Kansas City.
The addition of Diekman puts a second lefty in Chicago manager Tony La Russa's bullpen, joining rookie Tanner Banks. The White Sox also have Aaron Bummer, but he is on the injured list with a strained left lat.
Diekman was 5-1 with a 4.23 ERA in a team-high 44 games this season for Boston. His contract calls for $3.5 million salaries this year and next, and it includes a $4 million team option for 2024 with a $1 million buyout.
Bloom said he could make more moves before Tuesday's deadline.
"I don't know yet what is to come, but as with anything, we have to be open to what is right for the organization," he said.
Information from The Associated Press was used in this report.