With defensive pace setter Justin Smith down for the count with an untimely elbow injury, the proverbially under-the-radar Ray McDonald came to the rescue in the Niners’ thrill-a-minute 41-34 victory over the Patriots in Week 15.

McDonald came up with two of the Niners’ three sacks of Tom Brady, making his presence felt in a big way after being greatly overshadowed on the team’s D-line much of the season by Smith, who has been the same consistently relentless force as last season.

“He’s been solid, but his play has been a bit down this year, with hardly any sacks until the New England game after breaking out with 5½ last season,” one daily team observer said of McDonald. “There have been some opportunities (for sacks) — with (ROLB) Aldon ( Smith) and Justin getting manned up a lot of the time — that he hasn’t taken advantage of. But he’s remained real good against the run, and you could tell he was pretty fired up, especially after his late sack vs. New England.

“I’m sure the team was glad to see those sacks, too.”

The team also was no doubt happy to see reserve Ricky Jean Francois come up with a big sack in place of the injured Smith. The Niners face a big decision at nose tackle after this season, with both incumbent Isaac Sopoaga and the younger Jean Francois, who provides a bit more pass-rushing ability, eligible for free agency.

“Unless one of them would be willing to sign for the minimum, I can’t see the team signing both of them,” the observer said.

The Defensive MVP in LSU’s 2008 BCS championship game victory, Jean Francois has displayed impressive flashes on occasion.