Guetz and Mallinger both birdied No. 18 to reach 9-under-par 279 for the tournament, with Guetz doing it several groups after Mallinger to force the playoff.
Back at the par-5 18th, Guetz went for the green in two and then claimed his first Canadian Tour victory by rolling in a short birdie putt for the win.
'That was certainly a lot of fun,' said Guetz. 'You'll take the first one any way you can get it.'
It came courtesy of an errant drive by Mallinger on the playoff hole.
'It's basically the only tee shot that didn't set up for me all week,' Mallinger said after hooking his drive right into the woods. 'I just didn't feel comfortable on that box. I didn't commit to it in the playoff and ended up hitting a bad shot.'
It was the second week in a row that Barton Creek Resort hosted an event -- and for the second straight week a player won his first title in a playoff (Rob Oppenheim birdied the first hole of a four-man playoff at the Barton Creek Classic last Sunday).
The birdies by Guetz and Mallinger on 18 prevented what could have been a six-way tie for first place.
Craig Kanada, Omar Uresti, Jim Rutledge and Michael Letzig all tied for third place at 8-under-par 280.
Uresti, the 2005 champion and a runner-up last week to Oppenheim, chipped in from a ditch to eagle the 18th. But Mallinger and Guetz were both playing in later groups, and would soon both be at 9 under.
'That was an exciting day,' said Guetz. 'It was back and forth all day.'