Diary of a day spent watching the playoff for the 108th United States Open Championship, which turned out to be one of the most memorable in history:

11:43 a.m. — Turn on the TV in time to hear an interview with Rocco Mediate taped earlier. Rocco says this is going to be “the best day of my golfing career, win or lose. I’m going to go out there and have a blast. Everybody’s expecting me to not win. I can’t wait to see what I do.”

Me, too, Rocco. Me, too.

It’s hard not to root for Rocco, a congenial 45-year-old who’s never won a major, and isn’t likely to ever again have a better chance. And he is the unquestioned underdog against Tiger Woods. While Woods has won 13 major championships, Mediate hasn’t won a PGA Tour event since 2002 and missed the cut in seven of his first nine tournaments this year.

But how can you root against Tiger, who has been bothered all weekend by a sore knee, putting on a gutsy performance that included a 12-foot birdie putt on the par-5 18th Sunday to force this playoff?

Noon — Tee-off time. Tiger has played this opening hole, a par-4 of 448 yards, like a senior citizen from El Cajon, hacking his way to three double bogeys in the first four rounds.

Not today, though, as he pars and Rocco bogeys.

12:27 p.m. — There aren’t many people who have had a chance to hit a ball off Fenway’s Green Monster, shoot hoops in the new Garden, or throw the football around at Gillette Stadium, but anybody can play golf at Torrey Pines, a world-class, public course just up the interstate from downtown San Diego. I’ve played there several times, most recently when the Patriots were in San Diego in January 2007, for the AFC semifinal playoff game.

The par-3 third hole is strikingly beautiful, playing 188 yards downhill from an elevated tee overlooking the Pacific and fashionable La Jolla, just down the coast to the south.

After Tiger buries his 7-iron in the front-right bunker, Rocco nearly holes out a 6-iron, which roles just inches by the hole and stops a foot away. He takes a one-shot lead when he taps in his birdie putt and Tiger fails to save par.

I, ahem, had a two-putt par on that hole on my last visit to Torrey Pines.

12:56 — Among the reasons I love watching the Open is that it can make the world’s best golfers look like the rest of us. Exhibit “A” is Phil Mickelson’s quadruple-bogey nine on Saturday. On the par-4 5th, Rocco drives into a fairway bunker and then bounces his approach off two cart paths. He’s able to save bogey but loses his lead as Tiger pars to pull even at 1-over.

1:13 — On the sixth, which is regularly a par-5 but plays as a 515-yard, par-4 for the Open, Rocco hits a 5-iron approach, while Tiger parlays an 8-iron into a birdie and the lead.

As happens on almost every shot Tiger hits, somebody shouts “Get in the hole!” Is that really necessary? Especially when he hits his drive?

1:32 — A second straight birdie for Tiger, at the 461-yard, par-4 seventh.

1:42 — Tiger’s two-shot lead is cut to one as he again finds a bunker off the tee on a par-3 and bogeys while Rocco pars.

It was 10 years ago that I covered a playoff for the U.S. Open Championship at The Country Club, in Brookline, Mass. Curtis Strange won that one, shooting even-par 71 to beat Nick Faldo by four shots. Strange had to get up-and-down from a deep front bunker in order to par the 18th on Sunday and retain a share of the lead.

1:47 — Tiger didn’t grimace after his bogey, but he does when he tries to get something extra on the tee shot at the 612-yard, par-5 ninth.

1:58 — He’s all smiles, though, after he again goes up by two when he pars and Rocco bogeys.

2:06 — Tiger drives into the Kikuyu grass, which is native to East Africa. It is believed that the translation for Kikuyu is: “You haven’t got a prayer of reaching the green.”

2:13 — What Tiger is able to do is chip close enough to save par — unlike Rocco, who falls behind by three.

2:22 — What’s up with Tiger and the par-3s? Again, he finds a bunker off the tee, makes bogey and drops a shot.

2:37 — Another bogey for Tiger, this time at the par-4 12th. Rocco pars and — Hey! What’s this? — he’s only one behind.

2:58 — The par-4 14th is playing just 269 yards, which the announcers say leaves Tiger “in between” clubs. Presumably, that means it’s too short for him to hit driver, but too long for a 3-wood. Or, come to think of it, perhaps too short for 3-wood, but too long for a 3-iron. The idea that someone is “between clubs” at a distance of 269 yards is mind-boggling.

What’s even more mind-boggling is that Rocco gets up-and-down for birdie while Tiger has to settle for par and, with four holes to go, they’re all even.

3:14 — With Rocco on the green in regulation at the 478-yard, par-4 15th, Tiger pounds a fairway bunker shot inside Mediate’s approach. Amazing.

But is Rocco intimidated? No way. He rolls in his putt and Tiger — perhaps shaken? — misses, falling a shot behind with three holes to play. Mediate now has picked up four shots in five holes.

And so, the decision finally has been made — I’m rooting for Rocco now. I want to see the old guy hang on and pull off what would be a monumental upset.

3:31 — Tiger’s birdie bid at the par-3 16th comes up an inch short. An inch. Does that mean it’s Mediate’s day?

3:46 — Matching pars at 17. One hole to go, Rocco still leading by one after draining a nerve-testing, 4-footer.

3:49 — Oops. Rocco pulls his drive into the bunker left. He’ll have to lay up now in front of Devlin’s Billabong — the pond protecting the front of the 573-yard, par-5 18th. Tiger, wincing after he hit his tee ball, powers a long drive down the right side of the fairway. He was on in two Saturday, when he rolled in an eagle putt to seize the 54-hole lead, and now will be able to reach the green again in two.

3:57 —Tiger takes out a 4-iron and lands the ball on the green, albeit at two-putt distance. Rocco, attempting to become the oldest winner of a major tournament, hits his approach to 20 feet. What an incredible finish, with Tiger bidding for eagle, and Rocco having a chance to win it all with a birdie.

4:00 — Neither player makes his first putt, Tiger going 4 feet by; Rocco, three.

4:04 — Tiger, as he always does when it matters most, drains his putt.

4:06 — Don’t let Rocco lose this way. Not by missing a 3-footer. Whew. It goes in, and the tournament goes to its 91st hole. Which, in this case, is the 461-yard, par-4 7th.

4:15 — Tiger drives in the fairway. Rocco pulls his tee shot left, toward a fairway bunker.

4:19 — It may be over for Rocco, who pulls his approach toward the stands near the green. He gets a drop, amid chants of “Let’s go, Roc-co!” from the fans. Tiger, meanwhile, is safely on the putting surface.

4:26 — As on 16, Tiger comes up agonizingly short of a winning birdie. Rocco, following his pitch, has a 20-footer to keep the playoff alive. It slips past the hole.

It’s a truly great win for Tiger, who trailed heading into the final hole both Sunday and yesterday. But it would have been even more memorable had Rocco won.

jdonalds@projo.com