Mike Shanahan’s switch from Rex Grossman to John Beck as starting quarterback couldn’t ignite the Washington Redskins, who suffered another series of critical injuries to their starters Sunday as they lost, 33-20, to the Carolina Panthers at Bank of America Stadium.

A week after Grossman got the hook during a loss to the struggling Philadelphia Eagles, Beck took over — making his first start since December 2007 — but he and his increasingly battered team were defeated by a one-win opponent for a second consecutive week.

The once-promising Redskins did not have a lead against Carolina and fell to 3-3. Washington — which suffered its third defeat in the last four games — couldn’t find a way to slow the Panthers or match their offensive firepower.

Carolina rookie quarterback Cam Newton — the first overall pick in last April’s draft — embarrassed Washington with his arm and his legs. He completed 18 of 23 attempts for 256 yards and a touchdown and rushed for 59 yards and a touchdown on 10 carries. Newton’s Panthers racked up 407 yards (175 on the ground) and improved to 2-5.

Beck — who hadn’t started a regular season game since his rookie year — completed 22 of 37 passes for 279 yards and a touchdown to Fred Davis. He threw an interception and lost a fumble. The Redskins recorded 353 yards of offense, 92 on the ground.

“I’ve got to do a better job of getting these guys ready to play,” a disheveled Shanahan said at the lectern after the game. “We should’ve played better than that. But I take my hat off to Cam Newton. He did some things with his legs and made some throws that not even [seasoned] pros make.”

Even when fully healthy, Washington’s offense has struggled to execute consistently and to put points on the board. But the Redskins’ efforts were hampered against the Panthers from the start by the absence of injured offensive starters — tight end Chris Cooley, guard Kory Lichtensteiger and left tackle Trent Williams.

Then the Redskins lost leading wide receiver Santana Moss to a left hand injury late in the first quarter of Sunday’s defeat. And in the third quarter, they lost starting running back Tim Hightower, who was having a strong game with 17 carries for 88 yards, to a left knee injury. The Redskins didn’t know the severity of Hightower’s injury Sunday evening, but he was on crutches and wore a large brace in the locker room. He was scheduled to have an MRI exam on Monday.

On defense, where Washington already was without starting free safety Oshiomogho Atogwe, the Redskins lost inside linebacker London Fletcher with what the team said was a hamstring injury. One player speaking on condition of anonymity said Fletcher was suffering from a stomach virus and threw up on the sideline.

Along with the injuries, a late first-half turnover and failed third-quarter gamble served as the lowlights of Washington’s loss. The first came in the waning seconds of the second quarter.

After tying the score at 6 on a 49-yard Graham Gano field goal with 1 minute 2 seconds left, the Redskins got a stop from their defense and took possession with 46 seconds remaining in the half.

But on first down, wide receiver Jabar Gaffney dropped a deep sideline pass from Beck. On second down, Gaffney caught a pass over the middle but fumbled at his 34-yard line, and the Panthers recovered. Carolina place kicker Olindo Mare made a 45-yard field goal with two seconds left, giving the Panthers a 9-6 halftime lead.

On the first possession of the third quarter, Shanahan rolled the dice on a fourth-down play that ended up leading to the Panthers’ first touchdown. Facing fourth and two from the Carolina 40-yard line, Shanahan elected to go for it rather than punt, but Beck was swallowed up and sacked for a seven-yard loss, and the Panthers took over near midfield.

Newton and his offense needed only two plays to score. First, the rookie connected with wideout Brandon LaFell on a 37-yard pass down the left sideline. On the next play, Newton took the shotgun snap, faked the handoff and dashed 16 yards for the touchdown, giving his team a 16-6 advantage.

Shanahan dismissed the notion that the play had sparked Carolina.

“I don’t care if you go for it on the 40-yard line or you punt it and punt it to the 20. Sometimes you do things to put yourself in field goal range or for a touchdown. But you don’t go [57] yards in two plays. We’re better than that.”

Washington did respond to the Panthers’ quick strike, finally putting together a touchdown drive of its own. Beck went 4 for 4 — two completions to tight end Logan Paulsenand two to fellow tight end Davis — to march his team to the 4-yard line. On third and goal, a pass play broke down, but Beck took off and dived across the goal line for his second rushing touchdown in as many weeks to pull the Redskins to 16-13 with 8:14 left in the third quarter.

“Any time you score, there is a momentum swing in your favor and I felt from an offensive standpoint, when we were marching down the field, it felt like we were rolling,” Beck said. “. . . We were moving the ball the way you’re supposed to. So I felt definitely comfortable, like, ‘Okay, we can do this.’ ”

But Washington’s defense couldn’t get off the field on the ensuing Carolina possession. They were gashed for a 10-play, 80-yard drive capped by a two-yard run by Jonathan Stewart. The touchdown put the Panthers up 23-13 with 2:17 left in the third.

Newton spent much of the second half connecting with his favorite target, Steve Smith, who, after three catches for 41 yards in the first half, erupted for another four catches and 102 yards in the final two quarters against a tiring defense that also gave up 81 rushing yards in the second half. The Washington defense was on the field for 35 minutes 30 seconds.

“Cam was out there and did a phenomenal job,” Redskins safety LaRon Landry said. “He found all the holes in the defense.”

Beck completed a seven-yard touchdown pass to Davis to cut the score to 30-20 with just more than five minutes left. But with 3:21 remaining, Carolina’s Chris Gamble picked off a Beck pass intended for rookie Leonard Hankerson, who appeared to run a route that Beck was not expecting, sealing Washington’s fate.

The Redskins travel to Toronto next week to take on the Buffalo Bills, who are off to a surprising 4-2 start.

“When you get these losses like this, either you wake up from it, or you keep going down that tunnel,” said Davis, who had six catches for 80 yards and a touchdown. “I don’t think we’re that team that’s gonna keep going down that tunnel.”