The sold-out, three-game series at Yankee Stadium, which begins tonight, is the best-selling series on EBay Inc.'s StubHub. Fans are reselling tickets on the Web site for as much as $1,500 each. It's outselling the other intracity series between the Los Angeles Angels and Dodgers this weekend, as well as the other 13 matchups in Major League Baseball.

"The New York sports fan has just an unbelievable devotion for their teams and wants to be there," said StubHub spokesman Sean Pate. "They are much less casual than the rest of the country."

That devotion has the Mets and Yankees predicting they'll reach 4 million fans apiece this season, a feat only accomplished six times before.

Pate said twice as many tickets were sold on StubHub for the Mets-Yankees series than the one between the San Francisco Giants and Boston Red Sox, the second-ranked matchup this weekend. He declined to release the specific number of tickets sold.

The Mets and Yankees drew a combined 7.6 million fans last year to break the 7 million single-city attendance record set by the Los Angeles teams in 2005, according to Stats LLC, the Morton Grove, Illinois-based company that collects and sells sports statistics. New York, Los Angeles and Chicago, with the Cubs and White Sox, all set attendance records last season, Major League Baseball said.

The Mets this year are drawing an average of 44,600 fans a game, a 2.9 percent increase from record attendance in 2006, and are expecting 3.8 million to 4 million, said Dave Howard, executive vice president for business operations.

The Yankees, who have averaged at least 50,000 fans a game the past two years at 56,935-seat Yankee Stadium, are "hopeful" they'll break 4 million for the third straight season, said spokeswoman Alice McGillion.

Only the Yankees in 2005-2006, the Toronto Blue Jays in 1991-93 and the Colorado Rockies in 1993 have drawn more than 4 million fans.

This weekend's series is the second of the season between the New York teams. In the first, in May at the Mets' Shea Stadium, a total of 168,000 fans watched the Yankees lose two of three sold-out games. Shea has a capacity of 57,343.

This weekend, the Mets will face a Yankees team that has won nine straight games. The Mets, who have lost five in a row, lead the National League East by two games over the Philadelphia Phillies, while the Yankees trail the Boston Red Sox by 7 1/2 games in the American League East.

Tonight, the Yankees will start seven-time Cy Young Award winner Roger Clemens, who won his first start of the season last week against the Pittsburgh Pirates. He'll face the Mets' Oliver Perez, who is 6-5. Rookie Tyler Clippard will pitch for the Yankees tomorrow against Tom Glavine, and Chien-Ming Wang will face Orlando Hernandez in the series finale.

The Yankees still have a 33-24 edge since interleague play began in 1997. The only time the Mets won the season series from the Yankees was in 2004.

The Mets attendance is also getting a boost because of the way it is marketing its new ballpark, Citi Field, which is set to open in 2009. The team's season-ticket base increased 22 percent to 22,000 this year after it offered current holders priority seating at the new stadium, Howard said.

The Yankees, who also will move into a new venue in 2009, aren't disclosing their ticket-selling plans, McGillion said.