The best Padres roster in at least a decade had one glaring weakness entering this weekend's Trade Deadline frenzy: the bullpen. That weakness is being addressed.

On Saturday, the Padres and Royals announced a deal that sends right-hander Trevor Rosenthal to San Diego in exchange for outfield prospect Edward Olivares and a player to be named. Players currently not on a team’s 60-man player pool are unable to be traded, but according to sources, that piece is expected to be a low-level pitching prospect.

Rosenthal owns a 3.29 ERA with 21 strikeouts and seven walks in 13 2/3 innings this year. In eight big league seasons with the Cardinals, Nationals, Tigers and Royals, he has posted a 3.46 ERA.

Olivares, an outfield prospect with upside, could be considered a steep cost for Rosenthal. The right-hander is 30 and will be a free agent after the season. But Olivares was deemed expendable as San Diego makes a push for its first postseason berth since 2006.

• Padres' Top 30 Prospects

In no uncertain terms, this is the most win-now move of A.J. Preller’s tenure as Padres general manager.

What they got

Rosenthal is a veteran presence in a bullpen that has seen key cogs Kirby Yates, Drew Pomeranz and José Castillo land on the injured list already this season. In their absence, the San Diego relief corps has slumped to a 5.35 ERA entering play Saturday night.

But Pomeranz (shoulder strain) was activated from the injured list on Saturday afternoon, and Rosenthal could join him in the bullpen as soon as Sunday, Padres manager Jayce Tingler said.

“We’re excited to have him in,” Tingler said. “[He has] a lot of experience at the back end of bullpens and closing games, and he’s been having a great year with Kansas City.”

Another appealing aspect of Rosenthal’s resume is his postseason experience: He reached the playoffs four times while with St. Louis and posted a 0.69 ERA in 23 appearances.

It’s unclear what role Rosenthal will fill in the San Diego ‘pen, though Tingler noted that Rosenthal would get “some of the tougher outs to get, later in the game.” He converted all seven of his save opportunities for the Royals this season.

Pomeranz has been equally effective, filling in for Yates, but the veteran left-hander doesn’t seem too concerned about when he pitches.

“Just tell me when you need me to pitch and I’ll be ready,” Pomeranz said after news of the trade on Saturday. “I think all of us are on that same page. We’re just ready to help in whatever spot we’re needed most to get to that final out.”

What they gave up

Ranked as the No. 20 prospect in a stacked Padres farm system by MLB Pipeline, Olivares outperformed that ranking during Spring Training and Summer Camp. He was a surprise addition to the Opening Day roster, but he batted .176/.222/.294 with one home run in 13 games this season.

The Padres were still high on Olivares when they sent him to Kansas City. But they didn’t envision regular at-bats for him, given the strong showings of Wil Myers and Trent Grisham this season. The same held true for their future, with prospect Taylor Trammell likely looming as an outfield piece in 2021.

Still, the decision to part with Olivares didn’t come easily.

“He’s a controllable position player,” said Tingler. “That’s a pretty big value. But in order to get something, you’ve got to give up something.”

Strangely enough, the Olivares deal marks the second time in two months that the Padres have dealt an outfielder (and eventually a pitching prospect) to the Royals for a reliever. In July, they sent outfielder Franchy Cordero and right-hander Ronald Bolaños to Kansas City for lefty Tim Hill.

What’s next?

The Padres probably aren’t done. According to sources, Preller is still actively in search of more pitching help. He’s also open to adding an impact bat, preferably an outfielder, but that seems less likely at this point.

As for Rosenthal, he’s going to be a free agent after the season, and it’s unclear whether the Padres would look to re-sign him. That’s not immediately in their plans. The decision to trade for Rosenthal was a move exclusively with 2020 in mind.

“We believe in this team,” Tingler said. “We believe we have a chance to win. We have an opportunity to go to the playoffs, and I think this move is consistent with the words out of A.J., myself and the entire organization.”

Those words were backed up by actions on Sunday. The Padres are in full-on win-now mode, and they’re not done shopping.

It’s entirely possible that Preller does not make another move ahead of Monday’s 1 p.m. PT Deadline. But it won’t be for a lack of trying.