SANTA CLARA, Calif. — If the San Francisco 49ers demonstrated anything in Monday’s 31-17 win over the St. Louis Rams, it’s that they are fully prepared to fight firepower with firepower when they encounter the all-out offensive assault of Peyton Manning and the Denver Broncos on the road Sunday night.

Given the state of their banged-up defense, they might have no choice.

The 49ers finished Monday’s win with six key defensive players on the sidelines.

It wasn’t just any six. It was their starting nose tackle (Glenn Dorsey), their best pass-rushing linebacker (Aldon Smith), their best run-stopping linebacker (Patrick Willis), their best all -around linebacker (NaVorro Bowman), their best cover corner (Tramaine Brock) and their nickel back (Jimmie Ward).

It didn’t matter, in large part because quarterback Colin Kaepernick was doing his best Manning impression, spreading the ball around like never before.

He got four wideouts (Anquan Boldin, Michael Crabtree, Stevie Johnson and Brandon Lloyd) and two tight ends (Vernon Davis and Vance McDonald) involved in a performance that produced season-bests in passing yards (343) and touchdowns (three).

“He really has that kind of confidence in all his receivers and his tight ends,” 49ers coach Jim Harbaugh praised after the win. “Everybody contributed.”

The 49ers were so potent through the air, they basically gave standout running back Frank Gore the night off. He rushed for just 38 yards as the 49ers, until they went into a ball-control mode late with a big lead, felt comfortable putting the game in the hands of Kaepernick.

“Nobody plays like this guy,” Harbaugh said afterward. “He always plays well. He keeps doing it, doing it, doing it. He’s everything you want in a quarterback.”

MEDICAL WATCH: ILB Patrick Willis left Monday’s win over the St. Louis Rams in the second quarter because of an injured big toe on his left foot. Willis had X-rays after the game, then went in search of a second opinion Tuesday. The 49ers are expected to provide an update on Willis before practice Wednesday. It is feared he suffered a turf-toe injury that could sideline him for Sunday night’s game at Denver. … G Mike Iupati got knocked out of Monday’s win over the St. Louis Rams in the third quarter with a concussion. Iupati will have to pass the NFL’s mandated concussion tests this week in order to be cleared to play in Sunday night’s showdown with the Denver Broncos. Iupati was replaced against the Rams by Joe Looney.

–QB Josh Johnson was re-signed by the 49ers on Tuesday after he had been released on the eve of Monday’s win so that the club could have a spot on their 53-man roster for special-teams standout S Bubba Ventrone. Ventrone was released Tuesday so that Johnson could rejoin the team and practice with the club during the week.

REPORT CARD VS. RAMS

PASSING OFFENSE: A-minus — Colin Kaepernick remained unbeaten on Monday Night Football by getting nine different receivers involved in a 343-yard performance. Three touchdown passes went to three different receivers. An “A” grade would have been warranted if not for a blooper-reel flub in the end zone when 49ers tight ends Vernon Davis and Vance McDonald, both open, collided and dropped a sure score.

RUSHING OFFENSE: D — Kaepernick turned three runs into 37 yards, but that’s pretty much all the 49ers could do on the ground against a Rams defense that was committed to stopping the run. Frank Gore and Carlos Hyde averaged less than two yards per carry, combining for 52 yards on 27 carries.

PASSING DEFENSE: A-minus — Facing a quarterback who had burned the Dallas Cowboys and Philadelphia Eagles for 702 yards on 59-for-99 accuracy in his previous two games, the 49ers held the St. Louis Rams’ Austin Davis to 236 yards on a 21-for-42 night. They also sacked Davis five times and returned an interception for a game-clinching score.

RUSHING DEFENSE: A — If the Rams had hoped to take some pressure off their young quarterback by running the ball, they failed miserably. Even without star run-stopping linebacker Patrick Willis for more than half the game, the 49ers limited St. Louis to 93 rushing yards on 24 carries, turning the Rams into a one-dimensional passing team.

SPECIAL TEAMS: A — Phil Dawson did it again from long distance and the 49ers held explosive Rams return man Tavon Austin in check. Bubba Ventrone, signed earlier in the week, made an immediate contribution in kick coverage as the 49ers put a greater emphasis on special teams by releasing their third quarterback in order to beef up the punt and kickoff units.

COACHING: B — The greatest fear in facing the Rams was a letdown following tough wins over the Philadelphia Eagles and Kansas City Chiefs. Sure enough, the 49ers found themselves behind 14-0 in the first half. But a key play call on an 80-yard touchdown pass late in the second quarter turned the game around, and the 49ers’ coaches were able to plug all the right pieces in places where injuries occurred.