MIAMI -- The Marlins took a major step toward rebuilding on Thursday by trading reliever David Phelps to the Mariners for four Minor Leaguers, including outfielder Brayan Hernandez, who had been ranked Seattle's No. 6 prospect by MLBPipeline.com.
One of the most coveted relievers on the market, Phelps had attracted the interest of roughly 11 clubs in recent days. But a match was made with Seattle before Miami traveled to Cincinnati for a three-game series against the Reds that begins on Friday.
The Marlins also received right-handers Brandon Miller (the 16th-ranked Seattle prospect), Pablo Lopez (22nd-ranked) and Lukas Schiraldi, son of former big league pitcher Calvin.

Moving Phelps was expected, especially after the Marlins went 1-5 on their homestand coming out of the All-Star break. With a 42-51 record, Miami is 14 1/2 games back of the Nationals in the National League East and 11 1/2 games off the pace for the second NL Wild Card spot.
"As we approach the Trade Deadline, relievers often carry a lot of value," Marlins president of baseball operations Michael Hill said. "We had gotten several calls on David Phelps, and things started to pick up speed with Seattle that led to the deal as you see it. We got back four players that we really like that will head into our system and help to create more depth for us in the Minor League season."
Phelps broke in with the Yankees and was dealt to the Marlins, along with third baseman Martin Prado, after the 2014 season.
Phelps, 30, developed into Miami's most versatile pitcher, starting, pitching long and setup relief and occasionally closing. He was primarily an eighth-inning setup man this year, and was 2-4 with a 3.45 ERA in 44 games. The right-hander struck out 51 in 47 innings.
Phelps is the second core player from the past few years to be dealt by the Marlins. Shortstop Adeiny Hechavarria was dealt to the Rays for two prospects on June 26.
Miami maintains it isn't interested in dealing its contractually controllable core players, which includes outfielders Giancarlo Stanton, Christian Yelich, Marcell Ozuna and catcher J.T. Realmuto.
Phelps is making $4.6 million this year, and he has another year of arbitration eligibility before qualifying for free agency in 2018-19.
Closer AJ Ramos is attracting trade interest and is expected to be dealt before the July 31 non-waiver Trade Deadline.
"I think I'd call it very comparable to the David Phelps market," Hill said of interest in Ramos. "AJ has been one of the best closers in the game over the past few years. He's done a great job for us. As clubs look for pieces to solidify their bullpens, he should be someone they have interest in. We'll see how things unfold."
By moving Phelps, the Marlins now will get a better look at some of their younger relievers, like Nick Wittgren and Drew Steckenrider, recently optioned to Triple-A, in late-inning roles.

The return for Phelps bolsters Miami's system.
Hernandez, 19, is a 6-foot-2, 175-pounder from Venezuela who has the potential to become an everyday big leaguer. At Class A Short-Season Everett, his slash line was .252/.306/.408 with two home runs and 15 RBIs. He was re-ranked by MLBPipeline.com as the Marlins' No. 5 prospect.
"He's someone we saw on the international market a couple of years ago," Hill said. "He was the top player coming out of Venezuela a couple of years ago. He's someone who we've had a familiarity with. When we had the ability to access him, we were excited."
Miller, 22, was a sixth-round Draft pick of Seattle in 2016. The right-hander posted a 9-4 record with a 3.65 ERA with 94 strikeouts and 23 walks in 101 innings. He has above-average command and throws around 92 mph. Re-ranked No. 14 in Miami's organization, he has a back-of-the-rotation projection.
Lopez, 21, is a 6-foot-3, 200-pounder from Venezuela who has a 95-mph fastball. He's thrown 100 innings with a 5.04 ERA at Class A Advanced Modesto. Re-ranked No. 19 among Marlins prospects, he will be part of Class A Jupiter's rotation.
Schiraldi, 23, draws comparisons to Miami reliever Kyle Barraclough because he both strikes out and walks his share of batters. A 15th-rounder in 2014, Schiraldi has 63 strikeouts and 27 walks in 37 1/3 innings this season. He will be in the bullpen at Jupiter.
When the season started, the Marlins had playoff aspirations, but now they're open to making deals with an eye toward the future.
"Obviously, this was something we hoped we could have avoided," Hill said. "Our expectation every year is to be one of 10 playoff teams and bring a championship to South Florida."