WORCESTER — Jason Thresher wasn’t focusing on his competition at the 107th Massachusetts Open Championship. He was fairly certain Mark Stevens stood at 4 under par, so he knew he could force a playoff with Stevens if he sank his 7-foot birdie putt on the 18th hole of the final round Wednesday at Worcester Country Club.

But Thresher just wanted to post a respectable score.

“Honestly on that last putt I wasn’t thinking about the championship,’’ said Thresher, who played in the day’s final pairing after leading the event after the first and second rounds. “I was 1 over for the day and I wanted to finish every round this week even par or better, so I didn’t want the course to beat me this last day.’’

Thresher calmly made the putt, finished with a three-day score of 4-under 206, and forced a three-hole aggregate playoff with Stevens.

The 27-year-old from Ellington Ridge Country Club in Connecticut quickly grabbed a three-stroke lead in the playoff — making a 25-foot birdie putt on the second playoff hole while Stevens made a bogey — and clinched his first professional victory before Stevens could finish out the last hole.

“It’s the next big step for me,’’ said Thresher, who earned $15,000 for the victory. “I’ve been close. Closest I was was last year, tied for third, in contention on the back nine.’’

Thresher struggled out of the gate Wednesday after posting rounds of 3-under 67 and 1-under 69 on the 6,637-yard layout. He made par on the first hole, double-bogeyed the second, bogeyed the third, and made par on the fourth.

“And then after there I really turned it around and played some solid golf,’’ he said.

Thresher birdied Nos. 5 and 7 and made par on the next 10 holes before the crucial birdie on No. 18.

Stevens entered play Wednesday with a two-day score of 140. He made two birdies on the front nine and bogeyed No. 6.

“I didn’t really feel great on the front nine, honestly, I was kind of steering it,’’ Stevens said. “And I holed out a bunker shot on 10, which was a huge momentum-starter. And then I committed to a swing thought on 12 tee, and I hit some of the best shots I think I’ve ever hit under pressure, maybe even in my life.’’

Stevens cruised on the back nine with birdies at Nos. 10, 12, 13, 16, and 17.

“I had a great back nine, I enjoyed it,’’ he said. “My caddie drove from Tulsa, Okla., to be here and he’s a really good friend, so just to be in contention and to have that opportunity is something I’ll never forget for my entire life.’’

Stevens added that his runner-up finish may be “a blessing in disguise.’’

“Because now I’m that much more motivated to be better for the next time I have that opportunity,’’ he said.

Former Lincoln-Sudbury golfer Matt Hutchins was the low amateur, finishing at 207. If not for a two-stroke penalty for improving his stance in a bunker on the 13th, the 19-year-old could have been the first amateur to win the Mass. Open since 1999.

“I was just trying to get into the uncomfortable stance,’’ said Hutchins, a member of the Chico State (Calif.) University golf team. “I guess I improved my lie or swiped the sand over and improved my stance.

“Everything happened so fast . . . it just kind of happened and my playing partner [Matt Parziale] was right there watching me. I mean he had a much better view than I had.’’

Parziale informed an MGA rules official of the infraction, and the official informed Hutchins of the penalty after No. 15. Hutchins took the news in stride, playing his final three holes in 1 under.

“I just tried to stay in the present and hit the best shot I can at that time,’’ he said. “It was a great day out there and I had a lot of fun.’’