The 21-year-old holed a 12 foot putt for birdie on the third time up the par 5 18th to hold off the challenge from Fox, who matched Klein in regulation with a superb five under par 67.
Klein, who began the day with a one shot lead from his playing partners Fox and Jared Pender, was unflappable in the benign and warm conditions of the final round at the New Plymouth Golf Club.
A regular contender on the Charles Tour, it meant a lot to Klein to win.
"It's big," he said afterwards. "I have been up there a number of times and never got there. Today I just hung tough and finally got it done. To have a bogey free weekend really helped. "
The champion was feeling a mixture of relief and after the tense sudden death.
"It was nerve-wracking especially after my first drive which went way left. I hung in there. He just missed his chance to win and then I finally got home.
"[On the final hole of the playoff] I slightly chunked a six iron and then had a putt that I knew really well, I've had that putt a few times before and I was pretty confident I'd make it.
"It's special to win especially with a crowd around 18 like that. I'll enjoy this tonight."
Klein, of German heritage, had a clinical game plan for the final round.
"I wanted to minimise mistakes, hit fairways and greens and take my chances, I was bogey free so it worked."
The shortest hitter of the three players by some distance played his own game and carded a four under par 68 to keep Fox (67) and Pender (68) at bay for most of the afternoon.
He held a two shot lead over Fox and Pender with four holes to play. But both of the challenging players both made birdie on the 15th and 16th to have scores in the lead group tied on 13 under par with two holes remaining.
Pender bogeyed the penultimate hole to trail by one down the last. Fox had the best chance to win the tournament in regulation with an eagle putt from eight feet but it came up short so the pair was tied on 14 under after 72 holes of Stroke Play.
Fox had another good chance to win on the second playoff hole but his putt from 10 feet sat on the lip.
The former New Zealand amateur rep hit his third tee shot down 18 way left and Klein made no mistake with his birdie chance to seal the win.
He came to the New Plymouth on the back of a nine under 63 to win the Hawera Pro-Am and the hot scoring has come down to a change it putter.
"It has definitely been a good change. I putted a lot better at Hawera and I carried that onto here. It is a big key to my game."
Klein, whose plans to study as a helicopter pilot have been put on hold with his recent success as a tour professional, has enjoyed a dream trip to the Taranaki region. His improvement in his game has been down to rededicating himself to the pro-game.
"I am playing smart. I am getting more coaching. I am getting more coaching and my course management is better. I have also changed my driver which is getting me out there and there is about 20m difference which helps a lot."
Klein claims the lion's share of the $40,000 prize purse on offer at the New Plymouth Golf Club.
Meantime, Fox was philosophical about missing his first Charles Tour title as his dream start to his rookie year as a pro continues.
"This is the best I have done here. David played really solidly today. I gave myself a couple of chances both in regulation and in the playoff and I missed the putt and he made his. I am obviously pretty disappointed to have missed my chances to win but all in all it was a pretty good day."
Local legend Grant Moorhead finished alone in fourth place while reigning Carrus Tauranga Open champion Jim Cusdin and 2011 Taranaki Open champion Joshua Carmichael shared fifth place.
Royal Auckland golfer Fraser Wilkin claimed the amateur title from Craig Hamilton (Omanu) by five shots.
Pre-tournament favourite Mark Brown bounced back in the final round with a three under 69 to climb to tied 10th.
Meantime in the women's division defending champion Emily Perry won by 13 shots after a two over par 74 in the final round of the Taranaki Energy Open.
She was delighted to win another title and get the ideal confidence boost ahead of the Queen Sirikit Cup in two weeks' time.
Courtesy of NZ Golf