HAMPSHIRE golf star Justin Rose believes Henrik Stenson is the man to beat for Olympic glory after the Open champion holed the longest putt of his career to remain firmly in contention in Rio.

Stenson added a second round of 68 to his opening 66 at Reserva de Marapendi to finish eight under par, two shots behind halfway leader Marcus Fraser of Australia.

The 40-year-old Swede defied torrential rain to hole from 12 feet for a birdie on the first and 58 feet for another on the second, but looked like giving at least one of those shots back when his tee shot on the next found the water.

However, after taking a penalty drop, the world number five "tickled" a fairway wood on to the front edge of the green and amazingly holed from 108 feet for the most unlikely of pars.

"It was an interesting start and an interesting finish, just a bit of ordinary golf in the middle," said Stenson, who birdied three of his last five holes but bogeyed the other two.

"It was tough teeing off in the wind and rain and we probably got three of the toughest holes in those conditions right at the start.

"Driver went maybe 250 yards on the tee shot on the second, I hit a four wood from 220 that pitched pin high and released over the back and holed from 50 feet for birdie.

"On the third both Rafa (Cabrera-Bello) and I drove into the water but I managed to tickle a four-wood up onto the front part of the green. You are just standing there praying for a two-putt bogey and before I know it that thing found the bottom of the cup.

"It's the longest putt I've made in my career. First of all it's hard to get a putt that long on any green in the world; maybe on the double greens at St Andrews you can find one."

Stenson's score solidified his position as pre-tournament favourite for golf's first Olympic gold medal since 1904, but he added: "There's a lot of golf still to play. I always prefer to be two ahead than two behind, but in 36 holes if you are playing good you can make up a few shots and I'm happy with the first two days.

"I saw that some guys were more nervous here but I felt the opposite because I was pretty clear on my game and what I was going to do. I felt less butterflies walking to the tee box than in some other events. I'm sure that will change if you have a gold medal on the line on Sunday afternoon."

Belgium's Thomas Pieters birdied the first three and last three holes in a 66 which left him a shot behind Fraser, who followed his opening 63 with a 69 containing four birdies and two bogeys.

Rose and France's Gregory Bourdy were four shots off the pace after matching rounds of 69, with Ireland's Seamus Power two strokes further back after a 67.

"I feel like I have another gear or two to try and find so it would be nice if it all clicks into shape when you need it," former US Open champion Rose said.

"Henrik is the man to beat I reckon. He's in good shape, he's ice cool and we all know when he gets into a rhythm like we saw at Troon he's a pretty special player."