MIAMI GARDENS, Fla. -- Miami Dolphins coach Adam Gase said Jay Ajayi "had a bad five days" earlier this season.

On Sunday afternoon, Ajayi had a strong 60 minutes, rushing for a career-high 204 yards as Miami upset the Pittsburgh Steelers 30-15 at Hard Rock Stadium.

Ajayi, who scored twice on 25 carries, became the first Dolphins 200-yard rusher since Reggie Bush did it on Dec. 18, 2011, at the Buffalo Bills.

"The offensive line kept opening creases," said Ajayi, who averaged 8.2 yards per rush. "I looked up, and I was at 140 (yards). I had some guys tell me, 'Let's go man! Go get two!'"

Two, of course, meant 200.

Ajayi's performance takes away some of the stench off the "bad five days" Gase referenced, which came when Miami named Arian Foster the starting running back after he was acquired late in training camp.

A 2015 fifth-round pick out of Boise State, Ajayi had expected to be Miami's starter this year after the Dolphins lost Lamar Miller in free agency.

When the job went to Foster instead, Ajayi pouted, and Gase punished him, leaving him home when the team traveled to face the Seattle Seahawks.

But Ajayi worked his way back, with Gase saying, "We all have a bad five days."

Ajayi has since had the walk-off run that beat the Cleveland Browns in overtime, and he had his big performance against the Steelers.

Those are the only two wins this season for the Dolphins (2-4), and it left the Steelers feeling embarrassed that they joined the Browns in such dubious company.

"No need to sugarcoat that -- we got beat soundly today," Steelers coach Mike Tomlin said. "Stopping the run is an emphasis point, and 200 yards (allowed to Ajayi) is not good."

The Steelers (4-2) survived an injury scare when quarterback Ben Roethlisberger sat out one series in the second quarter after hurting his left knee.

"It happened before I threw," said Roethlisberger, who was intercepted by Dolphins safety Reshad Jones on the play in question. "I felt something funny in my knee.

"I don't know anything yet (about the severity). We pray it's nothing too serious."

Roethlisberger returned in the third quarter but did not have one of his better games. He completed 19 of 34 passes for 189 yards, one touchdown and two interceptions. But he had just 73 yards passing through three quarters.

In the past three years, he is 14-3 at home but just 9-8 on the road.

Dolphins quarterback Ryan Tannehill outplayed Roethlisberger. Tannehill had fans calling for his benching a week ago, but he completed 24 of 32 passes for 252 yards and no interceptions against the Steelers.

Tannehill, who had been sacked 17 times in the first five games, was not dropped by Pittsburgh.

"It's huge when you can go through your progressions," Tannehill said.

Miami scored first, getting a 30-yard field goal. After forcing a Steelers punt to open the game, Miami capped a nine-play, 53-yard drive with Franks' kick.

Pittsburgh took an 8-3 lead on its next drive, getting a 60-yard touchdown on an end-around run by Darrius Heyward-Bey and a two-point conversion pass to Le'veon Bell.

The score came after the Steelers had been stopped on a third-down sack by Andre Branch. However, two penalties called on Miami -- including a defensive holding on cornerback Byron Maxwell -- kept the drive alive.

Another penalty -- this time for an illegal formation -- nixed what would have been a Miami touchdown pass to tight end Dominique Jones. Instead, Miami settled for a Franks 30-yard field goal.

Miami closed the half with a 16-8 lead on a one-yard touchdown run by Damien Williams. The TD was set up by a 39-yard pass from Tannehill to Jarvis Landry, who was tackled at the two by Artie Burns.

The Dolphins stretched their lead to 23-8 on a one-yard run by Ajayi in the third quarter.

Pittsburgh cut its deficit to 23-15 on a Roethlisberger 23-yard touchdown pass to Cobi Hamilton with 1:02 left in the fourth quarter.

But the Dolphins recovered an onside kick and Ajayi put the game away with a 62-yard touchdown run around right end.

"That last (Ajayi) play illustrated everything about this game and how hard we played," Dolphins left tackle Branden Albert said. "We were tired of everyone calling us soft. We played physical today. We made a statement."

NOTES: Steelers CB Artie Burns, a rookie first-round pick, made his homecoming at the same stadium where he played college ball for the Miami Hurricanes. ... Steelers DE Cameron Heyward (hamstring) missed a game due to injury for the first time in his career, including college and high school. He had played in 85 straight NFL games (49 starts). ... The Steelers were without several other key players, including WR Markus Wheaton, RT Marcus Gilbert and LB Ryan Shazior. ... Miami placed starting OLB Koa Misi (neck) on injured reserve, and he is likely done for the season. ... Miami was also without TE Jordan Cameron and CB Xavien Howard. .... Dolphins LT Branden Albert returned after missing two games, first with a leg problem and then an illness that caused him to lose 12 pounds. ... Dolphins LG Laremy Tunsil returned after missing Miami's previous game because he slipped in the shower on Sunday morning, injuring his ankle.