World No 1 has no time for a Day off

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.