A long rain delay yields a rainbow, but at the other end came a 6-4 home-opening loss for Washington at Nationals Park. (Jonathan Newton/The Washington Post)

En route to his first game at Nationals Park, Dusty Baker got lost. The Washington Nationals’ new manager had been eagerly anticipating Thursday’s home opener, but he prefers to use his sense of direction and smarts to learn his way around a new city. After he found himself near Joint Base Andrews and on the Suitland Parkway, he broke down and used his GPS.

“It’s pretty out there,” Baker said. “I was in Maryland and Virginia. ‘Welcome to D.C.’ signs, too.”

The Nationals and Baker will have plenty of time to find their way, but on this day their pitching was shabby and their offense was erratic in a 6-4 loss to the Miami Marlins. An 85-minute rain delay in the second inning sapped some of the announced crowd of 41,650 of its enthusiasm and the game of its energy.

“This is our third game,” Baker said. “Just be patient because that’s what I’m forced to do.”

If the Nationals hope to return to the playoffs following a tumultuous 2015, they need to feast on the weaker opponents in their division. And they also need the back end of their rotation to pull its weight. Tanner Roark, returning to the rotation after pitching out of the bullpen much of last season, allowed four runs in his rain-stunted season debut. The bullpen didn’t help, nor did the offense, despite the efforts of Bryce Harper and Daniel Murphy.

“We did a good job of giving ourselves chances,” said first baseman Ryan Zimmerman, who reached base three times. “We just didn’t get hits.”

Before the game, Nationals General Manager Mike Rizzo formally presented Harper with his 2015 National League MVP plaque before the game. He held it high in the air with both hands as fans roared.

“It’s definitely something that I’ll cherish,” said Harper, who also received his Silver Slugger Award and was presented a commemorative key to the city by Mayor Muriel Bowser. “It’s a new year. I’m excited to get back, get going and looking forward to the new year. And hopefully — as a team, as a group — we can get to where we need to be and can all stay healthy.”

More fanfare followed: a giant American flag unfurled on the field, a fighter jet flyover and Clydesdale horses parading on the warning track. The moment was especially memorable to the seven new Nationals on the roster and the five new coaches and manager.

“You’re not sure how many Opening Days you’re going to get in your career,” Murphy said. “You enjoy them.”

Once the game started, the Nationals fell behind quickly. Roark gave up four singles in a row, most on the ground, some broken-bat hits. The last single put his team in a 3-0 hole. The Nationals erased the deficit with one powerful swing by Murphy. With the bases loaded, he battled back down two strikes and smashed Adam Conley’s pitch to the right field wall, missing a grand slam by a handful of feet.

But Roark couldn’t find a rhythm on the mound, and his command was off. The long interruption didn’t help. Roark threw in the indoor batting cages during the rain delay. Baker asked him how he felt, and Roark indicated he was fine to retake the mound. Baker and pitching coach Mike Maddux let Roark do so after the delay, while the Marlins replaced Conley with right-handed reliever David Phelps.

“I still felt good,” Roark said. “I wasn’t tired or anything like that. My body still felt great.”

Roark gave up another run in the third inning — on yet another single. Baker pulled him after four innings and 99 pitches. He was replaced by Yusmeiro Petit, who gave up an RBI single to Phelps, handing the Marlins a 5-3 lead. In the seventh inning, new bullpen addition Matt Belisle also gave up a run.

“Nerves were high. They always are,” Roark said of pitching in his first home opener. “But it was an awesome experience to get out there. I wish I could’ve gone a little longer, but things happen, and you move on to the next one.”

After Murphy’s triple, the Nationals’ offense sputtered, going 0 for 11 with runners in scoring position.

Jayson Werth looked particularly astray at the plate. After two Nationals walked before him to load the bases in the first inning, Werth struck out, swinging at pitches outside the strike zone. He struck out in the third and grounded out in the fifth — both with runners in scoring position.

Murphy and Harper were the only Nationals to provide run-scoring hits. Facing a three-run deficit and with no one on base in the seventh, Harper clobbered a pitch from reliever Bryan Morris off the second deck. The few fans that remained in the cold and damp night cheered. They held their breath in the ninth when Harper flew out to the center field warning track in the ninth off Marlins closer A.J. Ramos.

“I thought it was 10 rows deep to tell you the truth,” Harper said of his loud ninth-inning out. “Maybe in June or July it’s possible, but it’s still an out. I didn’t hit it well enough I guess, and it’s part of the weather, and I’ll play to my strengths next time and hit the ball to right field.”