The Broncos climbed within seven in the final pre-season game on Matt Prater's 49-yard field goal with 4:44 to play and they regained the ball at the Minnesota 44 on a fumble with 2:03 left.
After reaching the 18-yard line, however, Denver's Brady Quinn threw three straight incompletions and the Broncos ran out of downs.
Minnesota quarterback Brett Favre did not play and Webb finished 5-of-9 for 100 yards.
The Vikings concluded the pre-season at 3-1 and will open Thursday night in New Orleans. It will be a rematch of last season's NFC title game.
Denver rookie Tim Tebow went 12-of-16 for 167 yards and a touchdown. Tebow suffered a fumbled snap in the first quarter and Minnesota's Erin Henderson returned it 35 yards for a touchdown.
The Broncos (1-3) will start the season at Jacksonville.