PHOENIX (AP) _ He's halfway there.

Mark McGwire hit his 31st home run Friday night, a grand slam that left the St. Louis slugger 31 homers shy of breaking Roger Maris' record.

McGwire, who in batting practice became the first player to hit a ball completely out of the new Bank One Ballpark, connected in the third inning off Arizona's Andy Benes.

The Cardinals were playing their 65th game Friday night, of which McGwire has played in 59. Maris had 26 homers in the New York Yankees' first 65 games while setting the mark in 1961.

McGwire leads the majors in home runs and RBIs (80).

It was McGwire's 11th career slam. He has now homered in his last 11 series, having missed last week's three-game set at Los Angeles because of back spasms.

McGwire has hit 15 home runs in his last 20 games. After striking out in the first inning against Benes, he hit a 438-foot drive during the Cardinals' eight-run third.

The distance of McGwire's drive in batting practice was given on the scoreboard as 560 feet, but stadium construction manager John Wasson estimated the distance at 510 feet.

It was the sixth of seven homers McGwire hit in 21 swings during batting practice. The ball landed on a ledge above the American flag in left center and bounced through a window onto Jefferson Street.

The 20-foot-wide ledge _ 483 feet from home plate and 89 feet above the field _ helps support a huge advertising panel that was opened to allow wind to circulate in the roofed ballpark. The roof also was open.

Thousands of fans jammed the left-field grandstand and balconies left and right of the scoreboard to watch McGwire's batting show before the game.