DEL MAR, Calif. (AP) - Zenyatta broke strongly from the starting gate and by the half-mile pole, jockey Mike Smith knew she was up for the challenge of maintaining her perfect record.

Zenyatta extended her perfect record to 18-0 with a neck victory in the $300,000 Clement L. Hirsch Stakes at Del Mar on Saturday in the second-closest finish of her career.

``She had it pretty much under control. She ran big,'' Smith said. ``The way she did it was really impressive.''

The 6-year-old mare defeated Rinterval in a two-horse duel to the finish line in the 1 1-16-mile race at the seaside track north of San Diego. She covered the distance in 1:45.03.

``It's a lot of pressure every time she runs because she is who she is - a great horse,'' said Jerry Moss, who owns Zenyatta with his wife, Ann. ``She's a miracle.''

Zenyatta won the Hirsch for the third consecutive year over the synthetic Polytrack surface. She was first by a head last year in the tightest finish of her career, and won by a length in 2008.

``She only does what she has to do,'' Smith said. ``She'll just run until she passes the last one.''

It was her fourth Grade 1 win of the year, to go with victories in the Vanity Handicap, the Apple Blossom on dirt at Arkansas' Oaklawn Park, and the Santa Margarita Handicap.

Zenyatta paid $2.20 and $2.10 as the overwhelming 1-9 favorite of 32,536 fans on a sunny, cool day at the shore. Afterward, Smith guided her along the grandstand so fans could get a close-up view, although with cotton in her ears to blunt noise, Zenyatta may not have heard all the cheers.

``She's a great star,'' Moss said. ``It's wonderful to see people celebrate that. She's really got the fans and she hasn't let them down yet.''

Hall of Fame trainer Bob Baffert came to the paddock to see Zenyatta even though he wasn't saddling a horse. Her other supporters included Bo Derek, composer Burt Bacharach, Hall of Fame jockey Julie Krone and Hall of Fame golfer Amy Alcott.

``I'm a fan along with these people,'' Smith said. ``I just happen to be sitting on top of her.''

Rinterval returned $3.80. There was no show wagering and a minus place pool of $94,675.39.

``It was a great day for me and my horse, and a great day for the champ,'' said Rinterval's trainer Eric Reed.

Princess Taylor was third and Spring Style fourth, followed by Dance to My Tune and Made for Magic.

``It was good to see Zenyatta win,'' said Paddy Gallagher, who trains Princess Taylor.

Zenyatta lingered next-to-last in the early going, with Rinterval leading the way under Rafael Bejarano. She kicked into gear approaching the stretch turn, when David Flores aboard Dance to My Tune floated Zenyatta four-wide.

``There were a lot of tricks,'' winning trainer John Shirreffs said, grinning.

Smith said he considered splitting horses, but erred on the side of caution and guided Zenyatta outside to find clear running room.

``I'll save all the daredevil stuff for that last one,'' he said, referring to the Breeders' Cup Classic in November.

She came up to Rinterval, who didn't give way easily, keeping the pressure on Zenyatta through the stretch. Smith waved his whip at her, but didn't use it.

Rinterval led most of the way under a slow pace.

``I didn't want to be in front, but she was comfortable,'' Bejarano said. ``She was going OK. I tried to wait, but she (Zenyatta) came up outside me and I had to go. If I could have waited a little more, maybe it would have been different. But the winner deserved it. She was good.''

Shirreffs didn't openly commit to running Zenyatta because he was cautious about how she would handle the surface. Two weeks ago, the track was closed during training hours because materials in the surface had separated, causing inconsistencies. She had trained over the track since Wednesday after arriving from her home base at Hollywood Park.

Shirreffs said he was assured by track officials that the surface would be in good shape.

Zenyatta won her previous start in the Vanity at Hollywood Park in June, giving away nine pounds to runner-up St Trinians. This time, she carried 123, conceding just four to four of her rivals and two to Made for Magic.

Zenyatta is being pointed toward defense of her title in the BC Classic, where she beat the boys last year. The $5 million race is Nov. 6 at Churchill Downs.