ORCHARD PARK — Reggie Bush spent his first five NFL seasons in New Orleans having difficulty breaking 100 yards and the perception that he was a part-time player.

It’s taken one season in Miami for the former Southern California star and first-round draft pick to show he’s capable of being an every-down threat.

Having already rushed for 100 yards three times this season, something he managed only once with the Saints, Bush stepped his game to a new level Sunday. He had a career-best 203 yards rushing in a 30-23 victory over the free-falling Buffalo Bills, who have lost seven straight.

“I don’t think any of the questions bothered me,” Bush said, referring to his critics. “Rightfully so, people should be questioning me, whether I can do it or not. But I knew given the opportunity that I could show I could be a good back.”

Matt Moore shook off a concussion by throwing two touchdown passes, including a perfectly placed 65-yard strike to Brandon Marshall that broke the game open on the Dolphins’ first drive of the second half. And Vontae Davis had two of Miami’s three interceptions.

In a game with nothing but pride on the line for two AFC East rivals playing out their schedules, Bush provided the spark. He capped his day with an electrifying 76-yard touchdown run with 5:41 left, and celebrated with a feet-first slide on a snow-slick field through the end zone.

The 203 yards matched his combined rushing total from his past two games, and ranks third on the Dolphins’ list.

And he’s already pushed his season-best total to 973 yards, which is nearly half of the 2,090 Bush had in New Orleans.

All that was missing for Bush to make the day complete was Tony Sparano, the Dolphins’ coach who was fired last week.

“This win is for him,” Bush said, in crediting Sparano for convincing him to sign with Miami last summer. “If it wasn’t for him bringing me here, I wouldn’t be here. I’d still be — I don’t know where I’d be.”

The Dolphins won in interim coach Todd Bowles’ first game, and improved to 5-2 in their past seven. They also claimed the edge over Buffalo in determining which team finishes last in the division.

Though both teams have 5-9 records, the Dolphins own the tiebreaker over the Bills in having swept the season series.

Buffalo’s in jeopardy of finishing last in the division for a fourth straight year. And rather than looking like the upstart team that got off to a 5-2 start this season, they resemble more the rag-tag bunch that got off to an 0-8 start in 2010.

“It’s like a tale of two seasons,” linebacker Chris Kelsay said. “I think we expected to win every time we stepped on the field. I don’t think we expect to win now.”

C.J. Spiller scored on a 24-yard rush and added a 3-yard touchdown catch.

Ryan Fitzpatrick struggled again. He finished 31 of 47 for 316 yards with two touchdowns — including a 2-yarder to Derek Hagan — and three interceptions.

Fitzpatrick has 12 interceptions and eight touchdown passes during the team’s seven-game skid.

“We haven’t played very well, and that starts with me,” Fitzpatrick said. “I’ve got to get better. That’s the bottom line.”

Receiver Stevie Johnson came to his quarterback’s defense.

“It’s not just him and it’s not a one-person show,” Johnson said. “We don’t think he had a terrible game. It wasn’t all on him. It was on us also.”

Penalties proved costly: Buffalo was flagged 11 times for 92 yards. And the Bills failed to convert a third-down chance for the second straight game against Miami. The Bills went 0 for 11 on Sunday after going 0 for 12 in 35-8 loss at Miami last month.

Bowles spoke with Sparano a day earlier, and said the former coach wished him luck.

As for enjoying the win, that can wait.

“I think when I’m about 75 or 80 years old, and I’m sitting in the rocking chair, and I’m retired and can sit back and reflect on it,” Bowles said. “But it was a great win, no doubt about it.”

Miami swept the season series between the two teams for a 21st time and first since 2008.