SANTA CLARA, Calif. -- On the heels of a three-sack performance against the Denver Broncos on Saturday night, San Francisco 49ers linebacker Marcus Rush entered his team's locker room to a chorus of hecklers.

Yes, Rush had just claimed the top spot on the list of preseason sack leaders in one game but that wasn't enough to take the focus off what he didn't do. Namely, Rush had Denver quarterback Paxton Lynch wrapped up for a fourth sack and let him slip away for a short gain.

"Yeah, I've already heard a lot about it," Rush said after the 31-24 win. "Some of those you can't take back obviously but I'll make sure I get him down next time."

Rush's near miss was, of course, much easier to laugh about considering that the 49ers still managed to win and that Rush was one of the most prominent performers in that victory. That much of Rush's success came against backups didn't mean much considering that Rush has been considered a backup himself for most of the preseason.

In fact, heading into the game, Rush was considered a long shot to make the roster after spending last season on the practice squad. According to defensive coordinator Jim O'Neil, Rush had performed well in practice through the first few weeks of camp, but it's hard to see that really translate for a pass-rusher until he can bring down the quarterback.

“You know, I wasn't here last year with Marcus," O'Neil said. "I think [outside linebackers coach] Jason Tarver has done a great job developing him. I know he has completely changed his body from Year 1 to Year 2. I see him as a complete outside backer. He can rush the quarterback, he can set edges in the run game and he's very good in pass coverage with what we ask him to do."

It's a feeling that Rush says he thinks about a lot. While the 49ers practiced with the Broncos last week, Rush took a little extra time to peek at the offensive practice film so he could see what kind of moves Denver pass-rusher Von Miller was working on. Rush took some notes on Miller's moves and even noticed something new Miller was using that he hoped to one day add to his own arsenal.

Such film study isn't unusual for Rush. According to O'Neil, on the day of the game in Denver, he walked into the film room to see Rush studying tape for more than an hour on his own.

"It's just good to see a guy put in the extra work and he's studying tackles and he's studying formations and then he goes out and he has a three-sack performance and he plays really well," O'Neil said. "For me, that was good to see. It's stuff that you guys probably don't see, but seeing him put in the extra work and then reap the rewards of it was nice.”

For a 49ers pass rush that lacked punch in 2015, anyone capable of stepping in and bringing down the quarterback on a consistent basis would be welcome on the roster. Rush might have spent last season on the practice squad but he points to that as a positive because it allowed him to work on his pass-rush technique against one of the league's best left tackles.

"I was going against Joe Staley so it gave me a chance to just work moves," Rush said. "I'm just perfecting my craft of pass rushing. I know I have the ability to, it's just a matter of perfecting it and having those main moves you can use, and being confident when you get on the field to be able to use them.”

With two preseason games to go, Rush will still need to add more strong outings to secure a spot on the 53-man roster. Aaron Lynch's four-game suspension undoubtedly helps his cause but the Niners still have others like Eli Harold, Ahmad Brooks and Tank Carradine ahead of him in the pecking order. If Rush can get some chances against starting-caliber players and enjoy similar success, it would only increase his chances.

"I think he's just a guy that's got an unbelievable motor and can compete and I think when you have an opportunity with Aaron being out and then Eli was out for a little bit there then Marcus takes advantage of his opportunity in there,"coach Chip Kelly said. "That's what we try to preach to our guys is that when you get an opportunity to play, you gotta go. I think he's shown up.

"The other thing is he's a really good special teams player for us so I think he understands if he's going to make this team it's as a special teams player and as a backup outside linebacker, but the stuff he's doing right now is really giving him a shot at making this football team."