Woods yanked his opening shot into the Barry Burn, looking on in disbelief as the ball dribbled into the meandering stream. He limped home with a 3-over-par 74 that left a daunting seven-shot gap between him and leader Sergio Garcia.
The world's best player has plenty of work to do this weekend if he wants to become the first in more than a half-century to win a third straight Open championship.
Garcia followed a brilliant 65 with a workmanlike, even-par 71, sinking the sort of testy putts that have bedeviled him through his career.
"I managed to not make many mistakes," he said. "I didn't play as well as yesterday, but I was quite consistent."
K.J. Choi, who has two PGA Tour wins in the last two months, made a spirited run at Garcia with a 69. The South Korean got within a shot of the top spot before a bogey at the brutal 18th hole left him two back at 4-under 138.
"I didn't think I would be in this spot going to the weekend," Choi said.
Canadian Mike Weir shot a 68, the best round of the day, and was tied for third at 139 with Spain's Miguel Angel Jimenez, who nearly made a hole-in-one.
Further back was Woods.
After opening with a fine 69, Woods stepped to the first tee with an iron in his hand, intending to play if safe on the 406-yard hole. The burn curls in front of the fairway, then fades away down the left side not much of a threat unless a player really messes up.
Woods did, his right hand flying off the club as a course worker frantically waved behind him, signaling the ball was heading left. Way left.
It bounced a few times and hopped into the creek.
Woods managed a weak, pitiful smile and slowly shook his head as he looked at his yardage book. He needed a do-over and wound up with a double-bogey 6 on the hole, a grim start to a 3-over 39 on the front side that knocked him off the leaderboard.
"It was such a poor shot because the commitment wasn't there," Woods said.
He closed with a bogey on the stingy 18th for a 1-over 143 at the midway point.
"I could have easily shot myself right out of the tournament," Woods said, "but I kept myself in there."