Lawrence Okoye proved his medal credentials with an impressive final throw in discus qualifying in the Olympic Stadium.
The 20-year-old produced a throw of 65.28 metres with his third attempt, the fourth furthest of the morning, to go through to the final automatically.
The former rugby player, who has deferred a place at Oxford to study law to concentrate on athletics, is appearing in his first major championship in his home town.
He improved his British record to 68.24m in May and his qualifying throw was little more than a metre down on Estonia's Gerd Kanter's longest effort.
Okoye knew his final throw was a big one, celebrating before the discus even landed, pumping his fists and roaring with delight before running over to his coach John Hillier.
"It was unbelievable, really tough. The standard this year is much higher than it's ever been," he said. "It took a lot to get through and I'm glad to get the job done.
"Tomorrow I have a bigger job to do with the big guys coming through. It's going to be tough to get amongst them but I am ready to do it."
Okoye admitted his emotion-fuelled reaction was a mixture of relief and delight.
"The two years I've spent doing this would have gone down the pan if I didn't get through," he added. "The first (throw) was so bad, but I came back and showed some character which is good. I will be ready come tomorrow."
Brett Morse and Abdul Bukhari failed to make it through to the final, the former registering only one legal throw of 58.18m and the latter getting a best of 60.08m.