By Tony Jimenez

TROON, Scotland (Reuters) - Soren Kjeldsen's subtle message to his British Open rivals was 'don't discount me from title contention' after the Dane bulldozed through the pack to fire a 67 in the first round on Thursday.

His four-under-par effort pushed the world number 50 within four strokes of leader Phil Mickelson of the U.S., leaving him happy in the knowledge that his all-round game was back to where he wants it to be after a brief spell of difficulty.

"The last 18 months were really good and then I played poorly at last month's U.S. Open and the WGC-Bridgestone Invitational in Ohio," Kjeldsen told Reuters in an interview held under bright blue skies at Royal Troon.

"But I turned the corner at the Scottish Open last week and now I'm feeling pretty good," he said after closing rounds of 66 and 70 earned a tie for 21st place in Inverness.

"I've worked harder over the last two years than I've ever worked before and it's nice that it's paying off. I feel really happy with everything now and the sky's the limit."

Kjeldsen had only one top-10 result on the European Tour in 2014 but then enjoyed a memorable summer a year later.

He claimed his first victory in six years by winning the Irish Open and followed that up with a hat-trick of second-place finishes at the Made in Denmark tournament, the Nordea Masters and British Masters.

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Overall, he strung together a career-best nine top-10 placings last season to climb the world rankings.

"Apart from winning, which is obviously really important, I think the fact I struggled for a while, and I found it really difficult for a couple of years there, coming out the other side of that at my age has been very encouraging," said Kjeldsen, 41.

"You do have dark moments when you think to yourself, 'Is that it for me?' To get through those moments is almost more satisfying than actually winning.

"Going from a point where you feel really weak out on the course to suddenly feeling very, very strong especially under the gun," said Kjeldsen.

"At the Irish Open I felt very strong going down those last few holes and to get to that point from where I was, that's probably been the best thing for me."

Conditions at Troon are unlikely to be better this week than they were on Thursday and Kjeldsen bucked the general trend by performing almost as well on the more tricky back nine as he did on the outward half.

The Dane mixed four birdies with a solitary bogey going out before he recovered from a dropped stroke at the 12th by picking up two shots in the last three holes.

"We'll probably never see the back nine play as easy as it was today," said the blond Kjeldsen. "We almost had it playing downwind and conditions were terrific.

"I drove it really well, played a couple of iffy iron shots but made a few nice putts. The key though was getting the ball in play off the tee, if you do that here you've always got a chance."

(Editing by Ken Ferris)