MIAMI GARDENS, Fla. >> Five years after losing Super Bowl LIV here, the 49ers’ return to Hard Rock Stadium cruelly coincided with their elimination from this season’s playoff contention — even before kicking off Sunday’s 29-17 loss to the Dolphins.

Earlier victories by the NFC West-leading Los Angeles Rams and the wild card-seeking Washington Commanders officially extinguished the 49ers’ minuscule playoff chances, projected at less than 1%.

Thus, the outgoing NFC champions are playing out the string. Their home finale is on Monday night, Dec. 30 against NFC-leading Detroit, then the 49ers’ season closes Jan. 5 at the Arizona Cardinals, who led the NFC West in Week 11 but were also eliminated from contention Sunday.

“We still have two weeks of football left, and if I have football in front of me, I’m going to play as hard as I possibly can, and I’m going to try to get the guys around me to do the same,” tight end George Kittle said.

Many hallmarks of this 6-9 season resurfaced Sunday: injuries to multiple starters, a season-high 11 penalties, no takeaways, special-teams woes, and a late-game interception of Brock Purdy, who was hit in the process of that midfield miscue. That all — and then some — spoiled the 49ers’ first meeting against the Dolphins at Hard Rock Stadium since 2016.

Coach Kyle Shanahan said the 49ers already dealt this past week with “the vibe” of being a non-playoff team, a fate essentially sealed after their Dec. 12 loss to the Rams. Sunday’s official pregame elimination had no bearing on this game’s approach, Shanahan and several players said.

Instead, Shanahan was dismayed by his offense’s “lack of concentration,” such as rookie Ricky Pearsall’s two illegal formation penalties in a four-snap span, as well as three unnecessary roughness penalties after halftime on defenders Talanoa Hufanga, Jordan Elliott and Deommodore Lenoir.

“Penalties killed us, (and) not taking the ball away,” linebacker Fred Warner said. “One takeaway in the last five games is just not going to get it done. I challenged the defense at half, saying we needed to take the ball away to win the game, and we didn’t do that.”

The last time they stepped on this field, the 49ers fell to the Chiefs 31-20 in Super Bowl LIV after Kansas City rallied in the fourth quarter and Jimmy Garoppolo infamously overthrew an open Emmanuel Sanders. This time, the 49ers’ last-ditch comeback ended when Purdy got intercepted with under two minutes remaining. The 49ers had pulled within 19-17 on Purdy’s 2-yard touchdown pass to Eric Saubert with 12 minutes to go.

“It hurts going through it, but I still have all the faith in the world in what we can do moving forward,” said Purdy, who completed 26 of 40 passes for 313 yards and met childhood hero Dan Marino during pregame warmups.

It wouldn’t be a 49ers defeat without more health issues, from a first-series exit by linebacker Dre Greenlaw (right calf, not left Achilles), to second-half leg injuries for left tackle Jaylon Moore (quadriceps) and left guard Aaron Banks (knee, medial collateral ligament). Linebacker Dee Winters, Greenlaw’s replacement, left late with a chest injury.

Greenlaw was making the second start in his comeback from his Achilles tear in February’s Super Bowl, and after exiting 30 snaps into his scintillating season debut, he was shut down after his right calf tightened. Shanahan, Warner and Bosa all said the 49ers need to protect Greenlaw from himself.

The 49ers’ offense struggled to run, and Patrick Taylor Jr. gained just 24 yards (on eight carries) as their fourth different starting running back this season.

Purdy wisely turned to stalwarts George Kittle and Deebo Samuel for vintage efforts. Kittle closed in on his fourth career 1,000-yard season, reaching 967 yards Sunday with 106 yards on eight catches. Samuel totaled 96 receiving yards (on seven catches) and 25 rushing yards (on five carries), and recorded only his second receiving touchdown this season by bounding through four defenders on a 16-yard catch-and-run for an early lead.

“George and Deebo, their heart and fight for our team and trying to get things going for us, you see it, and I’m very, very proud to play with them and their love for everybody on the field,” Purdy said.

The 49ers’ first drive after halftime defined their season in a nutshell: a starter got hurt (Moore), a galling alignment penalty was called (Pearsall’s second for illegal formation nullified Samuel’s catch-and-run to the 2), a third-down incompletion came after a bad block (by Spencer Burford in his left tackle debut), and a special teams gaffe surfaced (Jake Moody missed a 41-yard field-goal attempt).

In Sunday’s fourth quarter, Purdy’s offensive line consisted of rarely used backups on his blindside. Burford was at left tackle in place of Moore, who started a fifth straight game in place of Trent Williams. Nick Zakelj took over at left guard when Aaron Banks exited in the fourth quarter with a knee injury.

Sunday’s postseason elimination did not immediately turn Shanahan into a free-wheeling play-caller. He declined to go for it on fourth-and-1 on their opening drive, and he opted for a 21-yard field goal by Moody after a third-and-goal incompletion from the 3.

Dolphins coach Mike McDaniel, Shanahan’s longtime protégé, wasn’t any more aggressive. The Dolphins got five field goals from Jason Sanders, the last of which came with two minutes remaining.

The 49ers surrendered their only lead 3:20 before halftime, when Tyreek Hill scored on a 3-yard touchdown catch against Charvarius Ward, Hill’s Chiefs teammate when they beat the 49ers in Super Bowl LIV here. It was Tua Tagovailoa’s 100th career touchdown pass, and it put Miami ahead 13-7.

Samuel had put the 49ers ahead 7-3 with 2021-like dominance and determination on the second snap of the second quarter. He scored on a 16-yard catch-and-run, first catching it at the 10-yard line, then banging off a trio of defenders and ultimately dragging a fourth Dolphin across the goal line.

Such highlights have been too few from him and the 49ers this season.