One was the course. The tournament moved out of soggy La Costa Resort north of San Diego to the high desert of The Gallery Golf Club north of Tucson, a course that no one has played in competition.
The other was the day of the week.
Except for major championships, Mickelson couldn't recall the last time he arrived at a PGA Tour event on Tuesday. And not just because the World Golf Championship begins on Wednesday.
"I was trying to think about that on the way over here," Mickelson said. "I can't remember the last time I played a practice round."
As if this tournament weren't already enough of an unknown.
Golf's most fickle event gets under way on Wednesday morning with Trevor Immelman taking on Thomas Bjorn in the first of 32 matches, the first round that will determine who can survive six matches.
For Tiger Woods, the question is whether he makes it eight in a row on the PGA Tour.
To do so, he has to win six in a row at The Gallery.
"This has always been one of the tougher events to win just because of the nature of the format," said Woods, the No. 1 seed for the seventh time in this tournament. "Match play, anything that happens is unpredictable. Sometimes, it takes a great round to advance. Sometimes, you can shoot over par and advance. All I know is you have to beat one guy at a time. You don't have to beat a whole field. Just six guys."
The 64-man field assembled in the high desert of The Gallery Golf Club represents the best in the world from 17 countries. The only guy Woods cares about Wednesday is Ryder Cup teammate J.J. Henry, his first opponent.
How fickle is this tournament?
Woods won in 2004 during his worst season on tour, when he went through another overhaul of his swing. He was in top form two years earlier, winning the Masters and U.S. Open, yet he couldn't get past Peter O'Malley in the first round of the Accenture.
"You can shoot 65 and lose. You can shoot 73 and win," Henry said. "You never know what you're going to get. Of course, I know if I play Tiger and shoot 73, I might as well pack my bags."
Jim Furyk is the No. 2 seed and will play Brett Quigley. Third-seeded Adam Scott faces Shaun Micheel, while Mickelson has the No. 4 seed and will play fellow lefty Richard Green of Australia.
Mickelson is playing as well as anyone coming into the tournament, although he has never reached the semifinals. He won at Pebble Beach by five shots, and had a two-shot lead on the back nine at Riviera until losing in a playoff to Charles Howell III at the Nissan Open.
What he learned during that rare practice round Tuesday is that The Gallery will require slightly different shots than Pebble Beach or Riviera. Instead of what he calls that "chip runner" with the driver, he was taking full swings and launching the ball higher.
The altitude, some 4,000 feet, will cause players to use a half-club less, maybe a full club with the longer irons. And unlike La Costa and its spongy greens that had Mickelson, Woods and others hitting with less spin into the green, Lefty expects to be more aggressive.
What that leads to is anyone's guess.
All anyone needs to know about this tournament is the overall record of various seeds _ the No. 59 seed has a better record (10-8) than the No. 5 seed (6-8). In eight years of this event, the seeds of five winners were outside the top 10. One match Wednesday features Geoff Ogilvy and Steve Stricker, past champions who were seeded No. 55 and No. 52, respectively.
Woods is a pro at match play, even though most of his success came as an amateur.
He learned as a teenager how frustrating this format can be, taking on a kid named James Mohan in the Southern California Junior Match Play. Woods said he shot 69 that day, posted the lower score and got eliminated.
"I did't quite understand that," he said. "I just came home and told Dad, 'I shot a better score than he did, but he won the match. That doesn't seem right.' He explained it to me. We went out the next couple of days and played match play."
After that, it was rare when Woods didn't win.
He captured three straight U.S. Junior Amateur titles, followed by three straight U.S. Amateurs. His record at the Accenture is 23-5, and his singles record in match play including exhibitions is 36-11-2.
Jack Nicklaus believes Woods' amateur record is what has carried him to 53 stroke-play titles, including 12 majors.
"Each day is a tournament in match play," Nicklaus said. "And you've got to finish that day if you want to go to the next day."
Nicklaus also is proud of his match play record. The only match he says he lost in 1959 was the quarterfinals of the British Masters. He lost two matches in 1960, and only one in 1961.
"As a result, I was a lot tougher when I got to the tour and got to medal play," Nicklaus said. "When I had to finish a tournament, I was able to finish it. Tiger's record as an amateur was fantastic. He knew how to finish as a kid, and when he got here, he didn't have to go through that. Absolutely, that was no coincidence."
For all the lore over Woods' record in match play, he might be tougher to beat over 72 holes of stroke play. Furyk was asked whether he would rather face Woods in an 18-hole match or 18 holes of stroke play. It took him a while to find the answer.
"I guess the point there would be it's not really a good scenario either way," Furyk said.
After some more thought, he chose match play because "it's a little bit more volatile."