Matthias Schwab set the early pace at the Betfred British Masters, as tournament host Danny Willett was left rueing a costly finish to his opening round.
The Austrian mixed seven birdies with a lone bogey to card a six-under 66 at the Belfry and set the clubhouse target, while Willett threatened to match Schwab's total until three-putting his penultimate hole and then sending his final tee shot into the hazard.
Schwab was level-par after six holes, having cancelled out a birdie at the 13th by missing a four-footer to save par at the next, before posting five birdies in a six-hole stretch around the turn and then draining a 20-footer at the eighth - his penultimate hole - to move top of the leaderboard.
"I think it's quite a good score, I'm really happy and pleased with the score but also with how I played," Schwab said. "I kept it together, one bogey and seven birdies, so it's been a really solid day."
Schwab's closest challenge came from Scotland's Calum Hill, who started the week with a five-under 67, while Bernd Wiesberger fired a penultimate-hole eagle to jump within two of the lead.
Willett - playing alongside Wiesberger - took advantage of the par-five third and made a tap-in at the sixth to reach the turn in 34, before getting up and down from the rough at the driveable tenth hole to post a third birdie of the day.
The 2016 Masters champion holed a 12-footer to salvage a bogey at the 12th after taking two attempts to get out of the rough but rolled in from five feet to pick up a shot at the par-four next, with a 10-foot birdie at the 16th moving the Englishman within two of the lead.
Willett made a three-putt par at the par-five 17th and then sprayed his tee shot at the final hole into the water, although recovered with an up and down from the fairway to leave with just a bogey and post a three-under 69.
South African Louis de Jager briefly held a share of the lead after following a 25-foot birdie at the third with a long-range eagle at the par-five, only to bogey his final two holes to slip back into the group on four under.
Scotland's Robert MacIntyre, the highest-ranked player in the field, opened with a one-under 71 in the morning wave, as former world No 1 Martin Kaymer struggled to a two-over 74 despite posting five birdies in his round.
Watch the Betfred British Masters throughout the week on Sky Sports. Live coverage continues Thursday from 1.30pm on Sky Sports Golf.