But there was disappointment for Australia's Mark Hensby, who had started the day as co-leader with Irishman Harrington and American Cink.
Hensby had hoped to mark his 54th birthday in style but could not conjure any of the magic that led to 19 birdies over the first three days and a share of the lead.
Aiming to become just the second Aussie to win the event after Graham Marsh (1997) and the first to win a senior major championship since Stewart Ginn at the 2002 Senior Players Championship, he only made two birdies on Sunday.
He shot a three-over 73 to tie for fourth at five under with Thomas Bjorn.
"I felt comfortable, I must admit. Obviously, we all get nervous, but I just didn't get off to the start I needed to really contend," said Victorian Hensby.
"We just hit a few clubs that probably weren't the right clubs and hit it in some bad spots where it's hard to two-putt.
"Just couldn't get any momentum going. Just couldn't get the putter right today.
"Overall, I'm happy for the week. I had a good week."
Fellow Australians Cameron Percy (66) finished joint ninth at one under, while Scott Hend (70), Greg Chalmers (69), Steve Allan (72), Rod Pampling (73), Stuart Appleby (72) and Richard Green (73) all signed over the card.
Playing alongside Cink for the fourth straight day, Harrington shot a three-under 67 to finish 11 under on the Broadmoor course.
The Dubliner sealed victory by hitting his approach to eight feet on No.18, putting pressure on Cink, who trailed by one but sat 30 yards in front of him on the fairway.
Cink's approach landed on the precipice of a ledge, but spun backwards and did not come to rest until it was 35 feet away to set up a two-putt.
That made it advantage Harrington, who also two-putted to win his second US Open title in four years, adding that to a trophy case that also includes the 2007 and 2008 British Opens and the '08 PGA.
"It kind of validates your career," said Harrington.
"It validates the past in a lot of ways. You're reliving the past glories, hitting shots, waving at the crowds. People are coming out because they know you from the past."
The only player who threatened to get in the mix in this two-man show was Miguel Angel Jimenez. After opening with bogey, the Spaniard made eight birdies to pull within a shot of the lead.
But he bogeyed 18 for a six-under 64, still the best round of the tournament, to finish third, two shots back.
With The AP.
