The Pirates have not lost a single game in which Melancon has entered into a save situation since April 21, 2015 - a span of 80 games. Since Melancon inherited the full-time closing role in Pittsburgh, taking over for Jason Grilli in mid-July 2013, he has secured more saves than any other pitcher in the Major Leagues (96). Baltimore Orioles closer, Zach Britton, ranks second in that span with 88.
This season, Melancon is 1-1 with 30 saves in 45 games. He has allowed just seven earned runs in 41.2 innings pitched (1.51 ERA), and held opponents to a .205 batting average.
Since the start of the 2014 season, Melancon has converted 92.7 percent of his save opportunities, the third-highest mark in the Major Leagues behind only Britton (92.9%) and Cubs right-hander Aroldis Chapman (93.8%). His 114 saves in that span are the most in MLB.
The 2015 Trevor Hoffman National League Reliever of the Year, Melancon has pitched in the Wild Card game with the Pirates in each of the last three seasons, including a scoreless frame in 2015 vs. Chicago and in 2014 vs. San Francisco.
Originally a ninth-round selection of the New York Yankees in the 2006 First-Year Player Draft, Melancon appeared in 15 Major League games for New York before he was acquired by the Astros in 2010, along with utility man Jimmy Paredes, in exchange for outfielder/first baseman Lance Berkman. Melancon was then traded in back-to-back Decembers, going from Houston to Boston in December, 2011, and from Boston to Pittsburgh in December, 2012.
Rivero, 25, is 2-4 with a 3.67 ERA in 96 career games out of the Nationals' bullpen. Acquired from the Tampa Bay Rays, along with catcher Jose Lobaton, just before the start of the 2014 season, Rivero made his Major League debut for Washington on April 17, 2015. He collected three saves and 21 holds while posting 8.82 strikeouts per nine innings over the course of his career in Washington.
Hearn, 21, was selected by the Nationals in the fifth round of the 2015 First-Year Player Draft out of Oklahoma Baptist University. The lanky left-hander is 2-5 with a 3.27 ERA in 22 games (15 starts) in his Minor League career. This season he is 1-0 with a 2.79 ERA in 10 games (four starts) for the Rookie-level Gulf Coast League Nationals and the Single-A Hagerstown Suns.