ST ANDREWS, United Kingdom - Jordan Spieth sees fellow American Dustin Johnson as the main obstacle in his path to completing a clean sweep of the year's first three major titles.
The 21-year-old Texan has already won the Masters and the US Open and needs the British Open crown to stand a PGA Championship away from being the first player in the history of the sport to achieve the calendar-year Grand Slam.
But so far at St Andrews, he has played second fiddle to playing partner Johnson, the man he pipped at the post to win the US Open title at Chambers Bay last month.
After two rounds, Johnson leads at 10 under, with Spieth five shots adrift and needing a good round on Sunday to have a chance in Monday's delayed finale to the tournament.
He still thinks he can make it three in a row.
"I believe I'm still in contention," he said.
"I still believe I can win this tournament. I need a really solid round tomorrow, though, because Dustin is not letting up.
"He's the only one I can speak of, he and Hideki (Matsuyama) because I saw it first hand. Dustin is going to shoot a good round tomorrow with less wind, and I'm going to need to shoot a great round to really give myself a chance.
"To fall from two back to five back isn't exactly what I wanted on a Friday, but it could have been worse, could have been better.
"It is what it is, and if I can shoot something like 10-under in the last two rounds, I think I'll have a chance to win." Johnson is the player many believe should have won a major by now, having come close in all four Grand Slam events, culminating in his three-putt meltdown at Chambers Bay.
But he has looked by far the best player in the field over the first 36 holes at St Andrews.
Now he needs to build on that for Sunday and Monday in the weather-hit tournament.
He will head out in the final pairing of the day with England's Danny Willett, who will have had nearly two days of inactivity, having completed his second round on Friday before darkness fell.
The 27-year-old from Sheffield will be entering unchartered territory for him, but he says he relished the prospect of becoming the first English winner of the Open since Nick Faldo 23 years ago.
Top Scot Paul Lawrie, the 1999 Open champion, will provide plenty for the home fans to cheer about as he stands alone in third at eight under.
As fate would have it, he will play alongside fellow Scot Marc Warren who is one of six players tied at seven under.
The others are Australians Adam Scott and Jason Day Americans Robert Streb and 2007 Masters champion Zach Johnson, and 2010 Open champion Louis Oosthuizen of South Africa.