Tseng finished with a birdie on the par-4 ninth after dropping a stroke on the par-3 eighth.
The 23-year-old Taiwanese star won the LPGA Founders Cup on Sunday in Phoenix for her 14th LPGA Tour title and second in four events this year.
She led the tour last season with seven victories – including major victories in the LPGA Championship and Women’s British Open – and finished the year with 12 worldwide titles.
Oh, a two-time LPGA Tour winner who fought a hip injury the past two seasons, also had six birdies and a bogey on La Costa’s Legends Course.
Hedwall had seven birdies and two bogeys.
EUROPEAN TOUR: In Agadir, Morocco, Damien McGrane opened with 7-under-par 65 to lead the Hassan II Trophy by two strokes, while Robert Rock lost a chance to play in his first Masters Tournament by taking an 11 on the fourth hole.
Rock is ranked 57th and this year held off Tiger Woods to win the Abu Dhabi Championship.
He must finish first or second in this European Tour event to make the top 50 and assure a spot at Augusta National in two weeks.
He called it “a shame and a disappointment” that one hole cost him his Masters shot. He eagled the 17th but finished with 77.
Alejandro Canizares (67) is in second place.
Former Augusta State golfer Scott Jamieson opened with 72.
Having difficult days were major winners John Daly (77) and Michael Campbell (81). Oliver Wilson, another former Jaguar, also struggled, shooting 79.
NATIONWIDE TOUR: In Broussard, La., Will MacKenzie and Brenden Pappas each shot 8-under-par 63 to share the lead after the first round of the Louisiana Open at Le Triomphe Country Club.
Brett Wetterich is alone in third after opening with 64.
Augusta’s Scott Parel shot 66 and is tied for ninth. Aiken native Matt Hendrix had 70.
CHAMPIONS TOUR: Defending champion Tom Lehman, Fred Couples, Loren Roberts and Kenny Perry headline the field for the Mississippi Gulf Resort Classic at rain-soaked Fallen Oak.
The 81-man field includes 28 of the top 30 from last year’s Champions Tour money list and 16 players in the field who won at least one major championship on the regular tour. The 54-hole tournament begins today.