QUALIFICATION: First two in each heat, plus the next two fastest times.
Jimisola Laursen of Sweden controlled the first 200 metres and had the inside position at the bell lap, with Britain's Mark Hylton right behind. Boris Gorban held third at the halfway point.
It appeared that that relative order would hold up in the final. But Hylton was able to move in and pip Laursen for the win in 46.79, as the Swede clocked 46.82 for a season's best.
The long stride of Gorban made sure he would stay in the chase for one of the two final time spots, as he posted a 46.91 in third.
The top performer of all 400-metre runners competing in Lisbon, David Caines of Great Britain had a narrow lead over Spain's David Canal after the first 200 metres, and ran strongly the rest of the way for a 46.65 win.
The Spaniard ran wide down the final straight, almost allowing Sunday Bada to steal second on the inside. Canal prevailed in 46.85 for the other automatic qualifier, however, with Bada settling into a tie with Gorban for the two time slots after the first two heats.
Felix Sanchez of the Dominican Republic was in command as the runners converged to the inside, with Jamaica's Danny McFarlane running right behind.
The Jamaican was able to overtake Sanchez in the final metres, winning in 46.90 to Sanchez's 47.02.
Jude Monye of Nigeria looked poised to take third, but his energy gave out over the last 50 metres, allowing Robert Mackowiak of Poland in a 47.24.
James Davis, the top US one-lap runner on the Lisbon roster, eased to the pole as the leader after the first 200 meters, with Russia's Andrey Semyonov chasing right behind.
Off the final turn, Davis eased up a little too much, creating the needed opportunity for Sofiane Labidi of Tunisia to score a surprise win in a national record 46.93. Davis's 47.01 got the nod over Semyonov's identical time on the photo examination for the second automatic qualifying spot.
The Maebashi silver medalist, Milton Campbell of the US, had to take a momentary backseat to Bahamian Troy McIntosh over the first half of the race.
Off the final turn, McIntosh faded and allowed a neighboring islander, Davian Clarke of Jamaica, to slip in for second (47.20) behind the winning Campbell (47.09).