Pieters took a one-shot lead into the final round at Albatross Golf Resort in Prague and carded a closing 69 to finish 19 under par, a shot ahead of playing partner Adri Arnaus, the Spanish rookie’s third runners-up finish this season.
England’s Sam Horsfield was two strokes further back alongside defending champion Andrea Pavan, who surged through the field with a final round of 65, the joint-lowest score of the day.
Pieters partnered Thomas Detry to victory in the World Cup in Melbourne last year but had not won an individual event since 2016, the year he won a record four points on his Ryder Cup debut at Hazeltine.
“I’m relieved. It’s been a long time,” Pieters said. “It feels good to win again. I never doubted myself but it’s just been a long road of not feeling that great with the golf swing. It feels good to get back on track again and get another win.
“It’s difficult when everybody says you should be winning two or three times a year. It’s always nice to hear but can also be a negative sometimes because I always felt like I was underachieving, but hopefully, there’s many more like this.
“I felt like I was in control today, almost the whole day, and I kind of did my own thing.”
Pieters held a four-shot lead after going to the turn in 33 and picking up a fifth birdie of the day on the 12th but saw his advantage halved when he bogeyed the 16th and Arnaus made birdie.
Arnaus also birdied the 18th to ensure Pieters could not relax entirely but the 27-year-old safely holed his par putt from two feet.
“I’m really happy I got it done,” Pieters added. “What a great last three holes by Adri. Made that two-footer a bit nervy at the end.
“I’m pretty proud of myself the way I handled 15, I found myself in a really tough spot (after a wayward drive) and did the grown-up thing and took a drop and still made par. As I said the last two days I’m still learning.”