Dustin Johnson became the 20th player to reach world number one since the Official World Golf Ranking began, lifted by his victory at the Genesis Open on Sunday.

The American has five wins and 30 top-10s from his last 50 ranking events and thus overtook Jason Day, who enjoyed 47 weeks at the top.

‘I came here to put myself in a position to win,’ said Johnson, who totalled 17 under par at Riviera. ‘I wasn’t thinking about my ranking, I was focused on what it would take to win this golf tournament.

‘I believe in myself, I think I’m a great player. But the best in the world… I probably wouldn’t have said it until today, but now I can say it.’

Victory at Riviera was a long time coming for the 32-year-old, who posted top-fives in each of the last five years there, including a playoff loss in 2014.

‘To finally get a win at the Genesis Open feels good because I’ve finished second here a couple times, lost in a playoff, felt like I should have won a couple other times,’ he explained. ‘It’s definitely nice to win on a golf course that I really enjoy playing and a golf tournament I really enjoy.’

Big storms caused weather delays throughout the four rounds and Johnson had to rise at 4.30am on Sunday to begin a 36-hole marathon.

He shot an impeccable 64 in the morning to pull clear of the competition, then sailed home with a round of 71 to win by five shots over Thomas Pieters and Scott Brown.

Justin Rose, Wesley Bryan, Kevin Na, and Charley Hoffman shared fourth place on 11 under par.

‘Today was long, but sometimes 36-hole days are good,’ said Johnson. ‘I had 14 minutes from the time I signed my card to when I teed off again. We were trying to squeeze in 36 and the Tour did a great job with everyone getting through.’

Branden Grace shared 22nd place on six under par. The world number 17 started the week by shooting 67, but coasted along from there with rounds of 70 and 69 before a mediocre 72 on Sunday forced him out of the top 10.