The 29th-ranked Spadea came into the match with the ignominious distinction of being the highest ranked player never to have won a title.
Having turned professional in 1993, fourth seed Spadea finally managed to get his breakthrough against Kiefer.
"I'm quite excited," said Spadea.
"I'm 29-years-old. I guess this shows you can teach an old dog new tricks. I never realised that my focus was maybe not to do these kinds of things but this week it was."
"I'll have a different mentality from now on. I thought just being on the tour was fun. It's better late than never."
Spadea held on for victory even though he allowed the second set to slip away from his grasp after losing the tiebreaker 7-5.
He regained his nerve in the third to seal the win after two-hours and 44 minutes of gruelling play under bright sun in 86 degree temperatures.
