'My brothers and sister were here today and it was a family effort,' said Mallon, who collected $560,000 for the win. 'I couldn't even look at them all day today because I knew they were getting emotional, as was I.'
Mallon closed the event at 10-under-par 274, as she held off a hard charging Annika Sorenstam. The Swede closed with back-to-back birdies to polish off a round of 4-under 67 to finish at 8-under-par 276.
Mallon was the story, however. She played the final 25 holes at minus-9, without a bogey. In the final round, Mallon posted 10 one-putts and had no three-putts over the four rounds.
'It was the right time,' said Mallon of her putter getting hot. 'I just felt so good over the putter today and they weren't easy putts by any means. I just rolled the ball so well and the cup looked like a bucket. It was a great day for that to happen.'
Jennifer Rosales opened the round with a three-stroke cushion, but came undone midway through her round. She opened with a birdie at the first to move four shots clear of the field.
The 2004 Chick-fil-A Charity Championship winner then carded five straight pars to remain atop the leaderboard. Rosales started to fall back to the field.
She came up short of the green at the seventh with her second shot and was unable to get up-and-down for par. At the eighth, Rosales knocked her second shot to the back fringe, but could not save par from inside 20 feet.
That bogey dropped her to minus-6 where she was joined by Mallon and Kelly Robbins.
Mallon was biding her time. She had dropped in back-to-back birdies from the third to get to 6 under, then posted four straight pars.
Mallon, who also won the 1991 U.S. Women's Open at Colonial Country Club, finally moved atop the leaderboard with a 3-foot birdie putt at the par-5 ninth.
Around the turn, Mallon was briefly joined at minus-7 by Robbins. Moments after Robbins birdied the 12th, Mallon rolled in an 18-foot birdie try at 11 to regain the lead at Orchards Golf Club at 8 under.
Mallon remained hot as she dropped her second shot within 8 feet of the cup at the par-4 12th. She drained that birdie putt to move to minus-9, two strokes clear of Robbins.
The 41-year-old parred the par-5 13th before sinking at 18-footer for birdie at the 14th to get to 10 under, where she stood four shots clear of the field after Robbins dropped a stroke at the 15th.
Coming down the stretch, Robbins could only manage to par the final three holes. Rosales, who fell off the pace with bogeys at the 10th, 15th and 16th, was no longer in the race.
It was Sorenstam, the top player in the women's game, who was lurking. Sorenstam won this event in 1995 and 1996, with Mallon finishing second to her in '95.
Sorenstam, who won the McDonald's LPGA Championship three weeks ago, managed one bogey and one birdie over her opening nine holes. She dropped in an 8-foot birdie putt at the 10th to get to 5 under.
After a pair of two-putt pars, Sorenstam pitched her third shot to the par-5 13th within 7 feet of the hole. She sank that birdie to get within three shots.
Sorenstam had birdie putts at each of the next three holes, but was unable to convert any of them. She did turn it on late though. The Hall-of-Famer sank a 12-foot birdie try at the 17th and a 7-footer for birdie at the last to get to minus-8.
'I'm disappointed, but I can get over it, because I played so well and I gave it my all,' said Sorenstam. 'You've got to give all the credit to Meg, she played so well, and to shoot 6 under on Sunday at the U.S. Open, it doesn't get much better than that. I'm proud with 4 under, it just wasn't enough this year.'
Mallon two-putted for par at 15 and 16. At the par-3 17th, she missed the green right. She could only pitch her second on to the fringe, but calmly ran home her par-saving putt.
At the last, Mallon found the fairway off the tee and knocked her second shot on to the green. Leading by two shots, Mallon nearly drained her birdie putt, but ultimately tapped in for par and her second U.S. Women's Open title, making her the third oldest champion at this event.
'I've seen so many things happen over my career. I finished second twice at this tournament and that hurt a lot,' Mallon said. 'So I kept that in the back of my head, knowing you've got to play every hole and play every hole hard.'
Robbins ended with a 2-under 69 to take third place at 6-under-par 278. Rosales stumbled to a closing 75 and finished at minus-3.
'I'm still in shock what happened today,' Rosales said. 'I mean Meg played awesome. I just couldn't get anything happening. I started strong, birdied the first hole, but after the bogey at the seventh everything went downhill. I tried, I tried my best, hopefully next year.'
Curtis Cup teammates Paula Creamer and Michelle Wie tied for low amateur at 1-over-par 285. They were tied for 13th place with Patricia Meunier-Lebouc.