Warner, known for his strong performances in the 110-metre hurdles, placed sixth in his heat with a time of 14.38 seconds. But he recovered with a personal best in the discus, throwing 45.90 metres.
American Trey Hardee won the hurdles in 13.54 seconds, edging teammate Ashton Eaton, who came in at 13.56.
Hans van Alphen of Belgium took the discus event with a mark of 48.28 metres.
The final three events are slated for Thursday, culminating with the 1,500-metre race.
Warner set personal bests Wednesday in the long jump, high jump and 400-metres.
Pistorius denied shot at relay
Double-amputee runner Oscar Pistorius was on the track but didn't get to run in the 4x400-metre relay at the London Olympics. He never even received the baton because South Africa crashed out in the first heat Thursday morning.
Pistorius got onto the track but didn't get a chance to run because Ofentse Mogawane, running the second section of the race before him, collided with a Kenyan runner about 90 metres from the finish and fell.
The man known as the "Blade Runner" became the first amputee runner to compete in the Olympic track and field competition when he ran in the individual 400 earlier in the week, reaching the semifinals.
South Africa won a silver medal in the relay at the world championships last year.
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