The Nationals struck far in advance of the trade deadline Monday, acquiring the Kansas City Royals' closer for three minor leaguers. Herrera is 14-for-16 in save opportunities this year with a 1.05 ERA.
The 28-year-old right-hander joins a late-inning group that includes set-up men Ryan Madson, 38, Brandon Kintzler, 33, and closer Sean Doolittle, 31.
"For the front office to send a message to us this far ahead of the deadline, to try to get us some help in the bullpen, I think it's one of those situations where in April and May, the bullpen as a whole had a really heavy workload," Doolittle told the Washington Post. "You saw Madson and Kintzler land on the DL because of that. It's almost their way of saying, 'Here's some help. Here's some reinforcements.'"
Madson allowed two home runs in Sunday's loss to Toronto and Kintzler is out with a right forearm flexor strain.
Doolittle picked up the save Monday against the Yankees in the completion of a suspended game and has succeeded in 19 of 20 chances, posting a 1.37 ERA.
"For me, we have an all-star closer right now," manager Dave Martinez said. "So (Herrera) will be asked to do some different things."
On Monday, the Nationals and Yankees finally completed their two-game series from May 15-16, splitting the two games.
Washington (38-32) won the suspended game, which resumed in the sixth-inning with score tied 3-3. Rookie Juan Soto, who had not yet made his major league debut when the game originally began in May, clubbed a two-run homer to give Washington a 5-3 win.
New York won the second game 4-2 behind Sonny Gray and scoreless one inning stints from four relievers as the Nationals went 0-for-11 with runners in scoring position.
Baltimore (20-50) sends David Hess (2-3, 4.13) to the mound Tuesday against Jefry Rodriguez (0-0, 0.00).
The Orioles travel down the Baltimore-Washington Parkway on a rare high following Sunday's 10-4 win over the Miami Marlins.
Baltimore had dropped nine games in a row and had lost 11 straight at home, tying the club record.
The Orioles hadn't scored more than five runs since a 9-3 win over the White Sox on May 24 in Chicago, a span of 20 games.
"It was difficult for everyone," Sunday's starting pitcher Dylan Bundy told the Baltimore Sun. "We know what we are capable of, and we're not doing it right now. It was one of those days where we performed the way we should."
The Orioles collected 14 hits, six for extra bases. Third baseman Jace Peterson matched his career high with four RBIs, including a two-run homer. Mark Trumbo hit a solo homer and had an RBI-double for Baltimore, which had scored four runs or fewer in 18 of its past 19 games.
"Usually when the team's struggling as a whole, the pitchers get a little more comfortable on the other side, and they cruise through some of those innings," Trumbo told the Sun. "It's important to try and kind of peck away. I'd like to see a whole lot more games that look like this going forward. I think everybody would."
Hess had been solid before allowing five runs in 3 1/3 innings in his last start, a loss to Boston. He faced the Nationals May 30 and took the loss despite allowing just one run on four hits over six innings.