Siem, 31, recorded the first ace of the 2012 Wentworth tournament, and his first on the European Tour, which propelled him up the leaderboard, following birdies at the first and fourth holes.
However, three bogies in his closing nine holes halted the German's momentum, as he chased an unlikely second tour win and a first since 2004.
"It was a great start. It was just unfortunate, I'm a little bit sad about it, I didn't keep the confidence," Siem told reporters.
"I said to myself 'That's your day now, just believe in yourself.' Yesterday was so hard, it took so much confidence out of you with that wind. Even with good shots the ball went somewhere (else)."
Winner Luke Donald was the last player to record an ace at the second hole, playing in the same tournament in 2006, while Spanish Ryder Cup team mate Miguel Angel Jimenez bagged the last hole-in-one at the longer fifth hole in 2008.
Siem finished on five-under-par 283, after posting a three-under 69, pumping his fist in delight at the 18th after beating his best finish of tied-37th at the European Tour's flagship event in 2004.
"Top-10, in that tournament with that field, the first three in the world rankings, I think it's a very good achievement for me," said the world number 138, who earned 116,100 euros ($145,300) thanks to his tied-seventh position.