The thunder cracked overhead and torrential rain pounded like a stampeding herd on the 3,000 "breathable bubbles" that make up the translucent roof and sides of the Water Cube. A fitting backdrop for the storm inside.
A trawl back through every women's 400m freestyle from 1924 to 2004 reveals that the champion's winning time would have comfortably made the final four years on. No longer. Defending champion Laure Manaudou (FRA) made it through in last and 8th place, in 4mins 04.93. Her time would have won the title at any time in history barring 1988, when the legendary Janet Evans, of the United States, set a world record of 4:03.85. Manaudou saw to that in 2006 and in March 2007 claimed the world title. Now, she finds herself barely making it into the final to defend her Olympic crown.
Technology, timing, time-honoured advances, deep pools, higher targets and much more play their part as they always have, But we will leave Beijing with swimming history widely and deeply rewritten in all 32 Olympic events - that much is already clear. It is not just that three world records, one of them in heats, took to 54 the number of global standards cracked in the pool so far this year. It is not just that 16 Olympic records - more than half in qualification rounds - have already fallen in just three sessions out of the 16 scheduled at the Water Cube. What is unfolding down the ranks of the world's fastest fish is just as significant to understanding why the pace of progress in the pool is unprecedented.
Michael Phelps and his dolphin-kicking skills are the tip of an iceberg when it comes to progress. Take the men's 4x100m freestyle heats as a snapshot. The headlines went to a semi-"B" team of Americans (no slight intended) who set a world record of 3:12.23. If that was impressive, then consider the Britain team of Simon Burnett (who broke his own British solo 100m record with a 48.20 effort leading off), Adam Brown, Ben Hockin and Ross Davenport. Going in to the heats, the national record stood at 3:18.96. They celebrated Britain's first appearance in an Olympic final in that event for 12 years with a time of 3:13.69. Their time would have missed gold in Sydney 2000 behind Ian Thorpe's memorable hunting down of Gary Hall Jnr in that smashing guitars battle that produced the first US loss in history - by just 0.02sec. The British time would have won silver last time too, in Athens, and gold by a wide margin at any Games before Sydney.
Just four of the 32 finals have been held so far in the pool, while a further eight events have featured at qualification level. In some events coming into these Games, more than half of the best 30 efforts ever come from 2008. After the Games, the all-time lists will be transfigured. Here's a glance at what we watched rising from the depths of tonight's session, comparing Athens 2004, Melbourne 2007 and Beijing 2008, and the all-time lists:
What it took to qualify for the last 8:
Women's 400m freestyle
Men's 4x100m freestyle
What it took to qualify for last 16:
Women 100m backstroke:
Men's 200m freestyle:
Women's 100m breaststroke:
Men's 100m backstroke
Men's 100m backstroke