BALTIMORE, JULY 2 -- It took Zigbelle a half-mile to outrun her shadow today at Pimlico Race Course.

The 3-to-2 favorite, challenged heartily by Shining Prospect (5-1) most of the race, edged away over the final quarter-furlong to win by a head in the $39,850 Speed to Spare Handicap for fillies and mares, the opening-day feature of Pimlico's summer/fall meeting.

The five-furlong race, scheduled for the turf, was run on dirt after overnight rain saturated the grass course, bringing on the withdrawal of seven of 14 entrants. Zigbelle, the 120-pound highweight who broke from the rail, was clocked in 58 1/5 seconds on a "good" track after fractions of :21 4/5 and :45 2/5. Tulindas was 5 1/2 lengths back in third.

"It didn't make any difference, dirt or grass," said winning jockey Donald Miller Jr. "She can run on anything."

But Zigbelle was hard-pressed to shake off Shining Prospect and star apprentice Kent Desormeaux.

Zigbelle broke sharply and established a brief one-length lead before Shining Prospect drew abreast on the outside after about an eighth-mile. They opened a three-length lead over No No Basquette, matching strides into the turn.

As the front-runners swung into the lane, Shining Prospect poked her gray head in front before Miller tapped Zigbelle twice left-handed. The filly responded.

While Miller primarily hand-rode Zigbelle, Desormeaux was urging Shining Prospect frequently with right-handed strokes. She remained on even terms until the final strides.

"She broke bad," said Desormeaux, the nation's most victorious rider, of Shining Prospect. "She sort of tripped up leaving the gate, and it probably cost us the race. In a five-furlong race, there's not enough time to make up for mistakes."

Miller was assigned Zigbelle by trainer John Robb, who saddled the filly for the first time after acquiring her from Jane Miller's stable. Donald Miller had ridden the 4-year-old bay daughter of Danzig early in her career.

"When she was young, she used to be real temperamental," Miller said. "Now, it seems she's a bit more honest. I wasn't real sure how she'd react to the whip, but I knew she'd been ridden by Jimmy Edwards in her previous races, and he's a lot stronger than I am."

Zigbelle's resolve was worth $25,903 to Run Rite, Inc., headed by Patrick Wilbourn of Middleburg, Va. Her second stakes victory of 1987 boosted her career earnings to $137,054.

Desormeaux won both daily double races today, astride favorites Mantau Mill ($4) and Sparkly ($6.20). Desormeaux, the leading jockey at Maryland's last two meetings, has won each half of the double three of the last four racing days . . .

The $350,000-added Suburban Handicap will be simulcast to Pimlico from Belmont Park Saturday. The race, Pimlico's ninth on a card of 11, features Broad Brush, who earned top weight of 126 among the five-horse field. The all-time Maryland-bred money winner, scheduled to be ridden again by Angel Cordero Jr., will be opposed by Lac Ouimet (under 117 pounds), Bordeaux Bob (112), Set Style (112) and Summer Tale (107) . . .

A total of 1,490 thoroughbreds have been nominated for the second Maryland Million, Sept. 19 at Pimlico. The nominations are rich in 2-year-olds: 354 males, 334 females.

The nine-race program, which totals $1 million in purses, was designed to promote Maryland's breeding industry. Entrants must be sired by a nominated Maryland-based stallion.