Wiese scored 13 runs and restricted Oman to 10 in the super over after the match was tied at the end of each team's 20 overs.
Namibia claimed a heartbreaking victory over Oman in their T20 World Cup Group B clash in Barbados after a low-scoring thriller was decided by a super over.
David Wiese was Namibia's hero in Sunday's final match, contributing 13 runs in the Africans' super out of a total of 21 before restricting Oman to 10 runs with ball in hand to seal a crucial victory in Kensington Oval.
The match had gone to decisive extra time after a tense duel in which both teams finished with 109 runs from the allotted 20 overs.
Oman looked headed for defeat after a superb four-wicket bowling display from Ruben Trumpelmann saw them all out for 109 off 19.4 overs.
But the Oman bowlers responded with a disciplined performance to hold off the Namibian batsmen, with Mehran Khan conjuring a magnificent spell to leave the match on a knife edge.
Khan finished with figures of three wickets for seven runs in three overs.
The veteran Omani bowler took two wickets in the final over to frustrate Namibia, who only needed five to clinch victory.
“Emotionally exhausting night”
But Khan was strangely overlooked by Oman during the super bowling duties, and was handed the ball by Bilal Khan.
However, that move backfired spectacularly, with Wiese hitting a four off the first ball and then bowling a full toss for six off Khan's second delivery.
Wiese took three more runs off the next two balls before Namibia captain Gerhard Erasmus hit four in a row to give Oman a daunting victory target of 22 in their super over.
Wiese took over the bowling duties for Namibia and, after conceding just two runs in his first two deliveries, took the wicket of Naseem Khushi.
Two more singles left Oman needing 18 off the last delivery to win, meaning Wiese was able to allow Zeeshan Maqsood to score six knowing victory was assured.
“I definitely aged a couple of years tonight,” Wiese, 39, said. “And I don't have many years left. “It was an emotionally draining evening.”
Wiese said he was confident of leading Namibia to victory with bat and ball in the super over.
“It helped me to get a feel for the game and know that if I got a few hits in the super over… then with the ball, I felt like taking the ball and executing.
“The course was difficult and did not play as we thought. But we adapted well.”
Oman captain Aqib Ilyas rued a near miss but defended the decision to opt for Bilal as the super bowler instead of the in-form Khan.
“I think Bilal is one of the best players you can have at this level,” Aqib said. “But there are days when you plan and it is not executed.
“He was clear, we were clear, but maybe the ball was wet and he couldn't execute.”
Earlier, Trumpelmann had given Namibia a dream start with two wickets in the first two deliveries of the match, part of a four-wicket performance. Wiese also impressed in the regulation 20 overs with 3-28 in 3.4 overs.
However, Namibia did a great job in the run chase, with Jan Frylinck (45) and Niko Davin (24) top scorers as the South African team fell just short of their goal of victory.
