Great Britain's Jess Varnish and Victoria Pendleton set a cycling team sprint world record in qualifying only to see China better the mark moments later in the opening Olympic event at the London 2012 velodrome.
The eight fastest teams advanced to the first round, with Varnish and Pendleton clocking 32.526 seconds to better the time Germany set in winning Track Cycling World Championships gold in Melbourne in April.
But China's Gong Jinjie and Guo Shuang went faster still in the fifth and final heat, clocking 32.447secs.
German duo Kristina Vogel and Miriam Welte were third fastest in 32.630, with Australia's Anna Meares and Kaarle McCulloch fourth quickest in 32.825.
The four fastest teams from the first round were set to go through to the medal rounds in an event which was wide open.
Jason Kenny and Sir Chris Hoy entered the corresponding men's event as defending champions and teamed up with 19-year-old German-born Philip Hindes.
Hindes had a disastrous start to his Olympic career in the fifth and final heat against Germany.
The teenager wobbled out of the start gate and lost control of his bike before tumbling to the track at the beginning of the first bend as team-mates Kenny and Hoy rolled past him.
Britain were poised to get a second opportunity and the hosts' rivals had already thrown down the gauntlet.
Russia trio Sergey Borisov, Denis Dmitriev and Sergey Kucherov clocked 43.681 in the third heat, quicker than the Olympic-winning mark in Beijing.
France trio Gregory Bauge, Michael D'Almeida and Kevin Sireau went quicker, lowering the Olympic record to 43.097.