Silvia Bertolaccini used an eagle to wing to a two-under-par 71 and a one-stroke lead over Nancy Lopez yesterday after the first round of a $75,000 Ladies Professional Golf Association tournament.

Lopez, bidding to become the first to win five straight LPGA tournaments, became unnerved when one of her drives struck a spectator at the Locust Hill Country Club.

The spectator, Gary Mesolalla, 43, of Rochester, was hit on the head by Lopez's tee shot on the 10th hole but was not hurt seriously. Lopez, in tears, apologized to Mesolalla, who wished her well. She then hit her next shot into a sand trap and posted a double bogey for the hole, her first double bogey in 83 holes.

She struggled to a closing 39 but was still tied for second place.

"I'm very emotional," said the 21-year-old rookie sensation. "If I had killed him. I would have quit. I was still crying on the 11th hole."

Still, she came up with her 14th perfomance of par or better in her last 15 rounds.

Alexandra Reinhardt, Murie Breer and Sandra Spuzich all shot 72s on the cool, sunny day to share second place with Lopez.

Eleven players matched or broke par over the 6,202-yard course. Beth Solomon, M. J. Smith, Janet Coles, Cathy Morse, Kathy Cornelius and Kathy McMullen all matched par.

Bertolaccini, a 28-year-old Argentinian who won for the first time last year, eagled the 450-yard, par-5 fourth hole and birdied the fifth to move into an early lead with Lopez. However, Lopez dropped off the pace with her double bogey at 10.

At one point on the back side, six players shared the lead before Bertolaccini went ahead with a birdie on the 15th.

If Lopez wins the first prize of $11,250 tomorrow, she will become professional golf's all-time rookie money winner. Jerry Pate won $153,102 on the men's tour in 1976. A victory would push Lopez's total $234 past Pate.