Buena Vista did not score an offensive touchdown in the game. The Beavers' two touchdowns came on a 55-yard punt return by former Albert City-Truesdale prep Troy Nielsen and a 15-yard interception return by Bart Smith.
Smith's interception return gave Buena Vista a 16-7 lead with 6:43 left to play in the first half.
Upper Iowa closed the gap to 16-13 on a Mike Hatten 2-yard TD run in the third period. The extra point was blocked.
Martinez drilled a 47-yard field goal with 53 seconds left in the third quarter to put Buena Vista up 19-13.
Upper Iowa, however, took a 20-19 lead with 7:24 remaining in the game when Justin Manson hauled in a 67-yard pass from Ben Jass. Jeff Moody added the extra point.
Buena Vista then engineered its game-winning drive, going 71 yards in 5:45 to set up Martinez's field goal.
Jared Smith rushed for 112 yards on 32 carries to lead Buena Vista's offense. Kyle Colbert completed 6 of 14 passes for 59 yards. Shane Jacobson caught three passes for 34 yards.
Buena Vista won the time of possession battle over Upper Iowa as the Beavers had the ball for 33:32 to the Peacocks' 26:28.
Buena Vista's defense held Upper Iowa to just 134 yards rushing. Hatten, the league's leading rusher, had 131 of those yards.
Buena Vista, now 2-0 in the league and 2-0 overall, entertains Central this Saturday in a battle of unbeatens.