McGregor was one of five to beat the Barcelona record of Germany's Petra Rossmer, but her time of 3min 39.545sec was some seven seconds slower than her personal best set on Manchester's indoor velodrome.
McGregor, the world hour record holder, raced against Italy's Antonella Bellutti, who set a world 3,000m best of 3:31.924 in Colombia in April. Bellutti underlined her quest for gold with an Olympic record of 3:34.130, breaking the minutes-old best set by France's Marion Clignet on the 250m track.
"I am glad that is out of the way," McGregor said. "The first is always the toughest ride and I was troubled in the windy conditions because it affected the five-spoke wheel I was using." She meets New Zealand's Sarah Ullmer today.
Before the five-day track competition began on Wednesday, scores of cyclists said they did not expect to see many records broken on the temporary wooden track. Too sticky and too small, they said - but there was nothing but praise after riders recorded 13 times below the world or Olympic records on Wednesday and five more on the first event yesterday.
In the women's individual pursuit qualification, five riders, led by Bellutti, shattered the mark 3:41.509 set by Germany's Petra Rossner at Barcelona. Bellutti's time was 3:34.130. France's Marion Clignet clocked 3:35.774, followed by McGregor (3:39.545), Rebecca Twigg of the United States (3:39.849) and Judith Arndt of Germany (3:40.335).
The world pursuit champion, Graeme Obree, refuses "to climb into a hole" after his shock exit from the 4,000m pursuit. He is now concentrating on the 52-kilometre road time trial on 3 August - but his chances there are minimal against men honed on a constant routine of top-class road racing.
His manager, Frank Quinn, said: "I have told him that he should go away and build up some form for the defence of his world title at Manchester at the end of August."
Obree, struck by a virus in June, lost 6lb in weight and thus arrived in Atlanta nowhere near the peak that has taken him to two world titles and world records. He was demoralised by the world-record times, particularly that of the Italian Andrea Collinelli, who lost to Obree in the world final at Bogota last year. Only 11th in the time trial stage, he missed the cut for the top eight places.
Even his world title could be in jeopardy because Chris Boardman, who won the Olympic pursuit in Barcelona, is also seeking new targets after a punishing Tour de France.Reuse content