PITTSBURGH — The greatest season by a Pittsburgh Pirates reliever began with doubt.

About Mark Melancon’s command. About the state of his right arm. About his ability to close the door.

Standing in a quiet clubhouse on April 21 following a 9-8 loss to the Cubs — a game in which Chicago tagged Melancon for three runs in the ninth — Melancon calmly answered every question with the confidence of a man whose belief in himself wasn’t shaken even as his ERA ballooned to 8.53.

When pressed on if he was concerned about a fastball that was only topping out at 90 mph — a tick below his career average in the 92-93 range — Melancon’s voice betrayed a hint of the edge his teammates have known about for years.

“What is the drop in velocity?” Melancon asked. “I don’t pay attention to that. I’m worried about results.”

Six months later, the questions are all gone.

That shaky inning against the Cubs marked the launch point for one of the best summers by a closer ever. Melancon converted his next 35 opportunities on his way to a major league-high 51 saves, a club record for a franchise that dates to the Chester A. Arthur administration.

That total includes one of the defining moments of Pittsburgh’s 98-win season. Facing the Cubs against at Wrigley Field on Sept. 25, Melancon came on in the ninth to protect a two-run lead and boost Pittsburgh’s lead over Chicago for the top spot in the NL wild-card race.

A double and a triple put the tying run at third with one out. Nine pitches later, the normally reserved Melancon tossed his hat into the air in triumph after striking out Jorge Soler and Javier Baez.

“Every pitch he threw was right where he wanted to put it in a very heavy situation,” Pirates manager Clint Hurdle said.

Even if Melancon doesn’t exactly do it like some of his brethren. In a position filled with guys whose arms might as well be lightning bolts with ligaments, Melancon’s stuff is far less overwhelming. His fastball average of 91.3 was a career low, a full five mph lower than the two guys who followed him on the saves list, St. Louis’ Trevor Rosenthal and Jeurys Familia of the New York Mets.

And yet it hardly mattered. Opponents hit just .207 off Melancon, who was more exclamation point than question mark at the back end of one of baseball’s best bullpens — thanks to a cutter and a breaking ball that spends most of their time from his glove to home plate in a straight line only to veer off at the last moment.

“The curveball never gets there,” Cubs manager Joe Maddon said. “He’s been outstanding. I’ve seen him good in the past, but he seems to be healthy right now. He’s good. He’s really good.”

Something the Pirates have known from the moment they acquired him from Boston as part of a trade that sent hard-throwing closer Joel Hanrahan to the Red Sox. Melancon made the All-Star team in 2013 as a setup guy for Jason Grilli before moving to back end when Grilli struggled early in 2014.

The speakers at PNC Park blast AC/DC’s “Thunderstruck” whenever Melancon jogs to the mound, but it’s a bit of aural misdirection. Melancon beats hitters with brains more than bombast.

“When you can locate the ball, you don’t have to do all those other things that some of that elite group does,” Hurdle said.

It’s what enabled Melancon to make Soler and Baez look foolish while waving at pitches that never really threatened the strike zone. It was by design. While he’s a workout marvel — take a look at his neck when you get a chance — Melancon’s greatest trait may be the meticulous way he goes over a scouting report.

“He’s the most prepared guy I’ve ever seen,” said teammate Tony Watson, an All-Star himself while working the eighth inning in front of Melancon. “He knows what his strengths are and he absolutely knows what the hitter’s weaknesses are. He knows who is going to pinch-hit, who is coming off the bench, who might pinch-run, defensive situations that are going and he pitches to that.”

Melancon’s steadiness is perhaps the biggest reason Pittsburgh posted a major league-high 36 wins in 53 one-run games, a quality that tends to pay dividends in October.