One of Jason Day's goals at the start of the year was to retain the world No 1 ranking for the entire calendar year.

After less than two months, he's already facing a big challenge - and not just from one rival.

Dustin Johnson, coming off a third-place finish at Pebble Beach, and Phoenix Open champion Hideki Matsuyama both have a mathematical chance to reach No 1 by winning the Genesis Open at Riviera this week.

Johnson would need Day to finish around fourth or worse, while Matsuyama could reach the top only by winning and Day finishing about 25th or worse.

Tiger Woods in 2009 was the last player to start and finish a year at No 1.

Rory McIlroy was the last player to stay at No 1 for longer than a year, starting with his victory at the 2014 Bridgestone Invitational and ending when Jordan Spieth eclipsed him with a runner-up finish in the 2015 PGA Championship.

Just don't get the idea Day is consumed with the rankings.

"I said earlier that a calendar year would be great to go No 1, but I need to just focus on what I need to do because you can't really focus on staying No 1," Day said.

"The more you focus on the actual target itself, the more you attach yourself to it, you make mental errors out there, you get more frustrated, you do silly things on the course that you shouldn't be doing."

Johnson also had a mathematical chance to get to No 1 last week, but he would have had to win Pebble and have Day finish out of the top 50. Day tied for fifth.

Johnson also had a chance at the PGA Championship last summer, but he missed the cut and Day was runner-up.

Day doesn't have a lot of history at Riviera. The only reason he is playing is because of the tour's new "strength of field" regulation that requires most players to compete at an event they haven't been to in four years.

His best finish is a tie for 62nd.

He keeps reminding himself that he didn't have a great history at Bay Hill and The Players Championship before winning them both last year.

Legendary caddie dies

The European Tour lost another beloved caddie when Dave Musgrove died on Monday at age 74.

Musgrove and Dave Ren-wick, who died last year, are the only caddies to work for three major champions.

Musgrove was on the bag when Seve Ballesteros won his first British Open in 1979. He worked for Sandy Lyle when the Scot won the Open in 1985 and the Masters in 1988, and he was alongside Lee Janzen when he won his second US Open at the Olympic Club in 1998.

Musgrove renewed his partnership with Janzen in 2001 so that he could caddie in his 40th consecutive British Open.

Among the many players paying tribute on Twitter was Lyle, who said: "We wrote history together at The Open, The Masters and The Players Championship. We'll miss your humor and your stories."

Nicklaus tribute

The end of the Masters coincides with the start of Golf Channel's latest project, a three-part documentary on Jack Nicklaus.

The Golf Films project is called Jack, and it will air over three straight nights in prime time starting on April 9. It will feature nearly 100 interviews and hundreds of hours of archived film.

"'This is a project that Golf Films has spent years developing in order to comprehensively capture the career and legacy of golf's most accomplished champion," said Mike McCarley, president of golf for the NBC Sports Group.

The first part will focus on the early part of Nicklaus' career, including his relationship with his father, meeting his wife and early success.

The second part will look at the his playing career, highlighted by his 18 major championships. The final part looks at his legacy in the game, from the priority he placed on family to his golf-course design and work with Nicklaus hospitals.

The documentary is being produced by Israel DeHerrera, who also produced the three-part series on Arnold Palmer that was broadcast in 2014.

Race for Mexico

The first World Golf Championships event is around the corner in Mexico City, and this week will start determining who gets there.

The field will be determined by the top 50 in the world rankings after this week. Thomas Pieters (No 47) and Shane Lowry (No 51) are among those playing the Genesis Open at Riviera, which has the strongest field of the year so far.

The tighter race is the FedEx Cup standings. The top 10 after the Honda Classic will be exempt. Hudson Swafford at No 8 and Gary Woodland at No 11 are separated by only 61 points with two weeks to go. Rod Pampling, currently No 10, has not played in a WGC event since 2009.

On the European Tour, Pablo Larrazabal is holding down the 10th spot. He has to stay there at the end of this week to make the Mexico field.

Much like Chinese players in the HSBC Champions in Shanghai, the WGC-Mexico Championship is reserving a spot for the highest-ranked Mexican player. That would appear to go to Roberto Diaz, who lost in a playoff on the Web.com Tour last week in Colombia. That enabled Diaz to move from No 719 to No 462.

He's currently ranked 36 spots ahead of the next Mexican player, Rodolfo Cazuabon.

Among those playing the Web.com Tour event in Panama this week who could pass Diaz are Carlos Ortiz and Abraham Ancer.

Divots

Jordan Spieth's nine PGA Tour victories have come at eight tournaments. The only place he repeated was the John Deere Classic. Tiger Woods did not win the same PGA Tour event until his 10th victory at the 1999 Western Open ... The first team event on the PGA Tour since 1981 will have official prize money, but not world ranking points. The Official World Golf Ranking board denied a PGA Tour request to offer points at the Zurich Classic this year ... Charles Howell III has had 46 finishes in the top 10 since his last PGA Tour victory at Riviera 10 years ago ... Sahith Theegala of Pepperdine earned a spot in the Genesis Open with a 69 at Riviera on Monday to win the Genesis Open Collegiate Showcase.

Matsuyama hopeful row can be settled

Japan's world No 5 Hideki Matsuyama is still hoping a sexism dispute won't spell the end of Kasumigaseki Country Club as the venue for the 2020 Olympic golf competition.

Matsuyama didn't wade into the thorny debate, sparked when Tokyo's female governor, Yuriko Koike, said she felt "uncomfortable" with the idea that women couldn't become full members of the club - a fact that has also prompted concerns from the International Olympic Committee.

Amid calls to move the Olympic tournament, Matsuyama said he hoped that wouldn't prove necessary.

"There are some membership questions right now, but I played well there at Kasumigaseki, won the Japan Junior there, the Asian Amateur," Matsuyama said on Tuesday as he prepared for Thursday's start of the Genesis Open at Riviera Country Club in California.

"When I won there, that's kind of what made it all possible, why I'm sitting here today," he said. "So I hope they get things worked out and I hope Kasumigaseki will be the site of the Tokyo Olympic golf competition."

Matsuyama will tee it up on Thursday with a chance to rise from fifth in the world rankings to No 1. He'd need a victory, and even then it would depend on where current world No 1 Jason Day finishes.

He'll be playing for the first time since retaining his Phoenix Open title a fortnight ago with a playoff victory over former US Open champion Webb Simpson.

It was Matsuyama's fifth victory in his last nine starts.

AFP