Mallon's 270 breaks the previous record of 272 that Annika Sorenstam set in 2001. The 41-year-old Mallon also becomes the first person to win the U.S. Women's Open and the Canadian Women's Open in the same season.
Mallon is also the first player since Sorenstam to follow up a win in a major with a victory the following week. Sorenstam did that in 2001 when she ran off four straight wins, including the Nabisco Championship. Mallon is the fourth player to win the U.S. Open and the event immediately following, and the first since Se Ri Pak in 1998.
'You know, this is my 18th year on tour, and it's been such a rewarding career, but I've never had two weeks like this,' said Mallon, who earns $195,000 for the win. 'The experience, it's going to take a while to absorb. It's just been incredible. I don't know what to say.'
Beth Daniel, the 2003 champion, also posted a 2-under 70 to finish at 14-under-par 274. Jean Bartholomew and Lorena Ochoa shared third place at 12-under-par 276, with local favorites Lorie Kane and Dawn Coe-Jones one stroke further back at minus-11.
Mallon was never really threatened in the final round. She opened with pars on each of her first four holes. She then dropped in a birdie at the par-4 fifth on the Battlefield Course at Legends on the Niagara.
The 17-time winner on the LPGA Tour came back with a birdie at the par-3 eighth, a hole she birdied all four rounds, to get to minus-18. She parred the next three holes around the turn, something she also did all four days.
Mallon, who bogeyed the 12th and 13th during the second round, parred each of those holes in the final round to make it five consecutive pars.
The two-time U.S. Women's Open champion parred the final five holes of her round, to make it 10 pars in a row to close out her day.
Those two bogeys in the second round were Mallon's only two of the event. She finished with no eagles and 20 birdies to set the tournament scoring mark.
'I didn't have my finest game today, but John and I just put together a smart round of golf and made key putts early on,' she said. 'It was hard for me today. I've never had a four-shot lead going into a last round. I'm much more of a player that likes to come from behind and charge and go get them. So I had to figure out how mentally I was going to approach the day today. It was quite a challenge inside this little head of mine all day to stay focused like that.'
Daniel, who carded four rounds in the 60s last year to become the oldest champion of this event, was unable to make a run at Mallon in the final round as she dropped a stroke at the par-4 fourth.
Daniel erased the mistake as she dropped in back-to-back birdies from the sixth to get to minus-13. She then carded eight straight pars before birdieing the par-4 16th. She parred the final two holes to end alone in second.
'I think the first five holes told the whole story, because neither one of us started out real well,' Daniel said. 'Meg got it up-and-down a couple times from incredible places that you shouldn't get an up-and-down from. That's what it takes to win golf tournaments.
'Unfortunately, I couldn't get anything going in the beginning of the round and that's what I needed to do. I feel like my job for the rest of the field was to put some pressure on Meg and I was not able to do that.'