(REUTERS) - Thailand's Thongchai Jaidee opened his British Open campaign with an even-par round of 71 and believes his putter must improve drastically if he is to climb up the leader board at Royal Troon.

The 46-year-old, who became the oldest winner in European Tour's French Open this month, made two birdies on Wednesday, but a double-bogey on the 15th hole left him with much ground to cover, as he trails leader Phil Mickelson by eight shots.

The three-time Asian Tour Order of Merit winner said he needs to read the greens better to challenge the leaders.

"I missed a couple of chances on the second and third holes, hit good putts and didn't find the hole," he said in an Asian Tour statement.

"The greens are a bit tricky and you need to read the lines well. It's a putting challenge this week.

"You can attack the par fives on the front nine which are reachable and if you can score on those, it helps. Then you have to be careful on the back nine."

Thongchai was happy with his overall game, however.

"I played well except that I didn't get many birdies," he said.

"Even par is a good start but I expect Friday to be harder.

"I tried to make it confident, trying to hit fairways and greens but the winds were switching direction.

"Just two bad tee shots. I think it's still a good start."