The 20-year-old, playing her first singles final, dropped her first set in the tournament but rallied past Mattek-Sands 1-6 7-5 6-3.
"I was a little nervous at the start and couldn't get my serves in. That contributed to the heavy (first set) loss," Pliskova told reporters.
"I woke up in the second set and began to serve better. This helped turn the tide.
"It was a tough match but I'm delighted to win my first singles title. I still can't believe it."
Mattek-Sands got off to a flying start and looked set to win her first singles title in her fourth final but the big-serving Czech, ranked 127, found her way back into the match.
The match was tied 1-1 in the third and final set when a thunderstorm and rain halted play for more than 30 minutes on another hot and humid day in Kuala Lumpur.
"I'm still happy with the way I played all week. I don't think the rain delay affected me at all," Mattek-Sands said. "Just that she played very well.
"The beauty of tennis is that there is another tournament next week so I just have to pick myself up and get on with it."
Pliskova, who served 10 aces in the match, collected $40,000 in prize money.