Britain's Daniel Awde made a superb start to the gruelling decathlon with a personal best in the opening event in the Olympic Stadium.
Awde responded to the roars of another capacity 80,000 crowd with a storming run of 10.71 seconds in the fourth and final heat of the 100 metres, taking 0.14secs off his previous best.
He found himself under huge pressure in the decathlon long jump when his first two jumps were fouls, and was understandably well behind the board with his final attempt. The resulting distance of 6.83m was well down on his personal best of 7.47m and saw him drop to 19th overall.
There was good news elsewhere as Sophie Hitchon improved her own British record to give herself a chance of reaching the women's hammer final. Hitchon was set to bow out after a first-round attempt of 67.21m and a foul in the second, but the 21-year-old then produced a superb throw of 71.98m in the final round, 37cm further than her previous best.
Hitchon was delighted with her British record, saying: "I was just proud to be on the team and to come here at a morning session, with a full crowd and throw a PB and a British record, it was amazing."
Mo Farah did not have to wait to discover his fate after finishing third in the first heat of the 5,000m, the 10,000m champion safely advancing to Saturday's final as he aims to complete the Olympic long-distance double.
Farah's coach, Alberto Salazar, said he thought the 29-year-old had recovered well from his exertions in the 10,000m, but Farah was still made to work hard to advance in a time of 13 minutes 26 seconds.
"It was pretty difficult," Farah told the BBC. "I was a bit tired, it took a bit more out of me than I was expecting, but I'm really happy with where I am now and I've got a couple of days off.
"I kept getting caught, there was a lot of pushing and shoving going on, that's what happens in the heats. Hopefully it will settle down in the final. I'm going to go out and give it 110%, that's all you can do. It just depends how my legs allow me (to run)."
Britain's Nick McCormick actually ran quicker than Farah in the considerably faster second heat, but could only finish 12th in 13:25.70 to miss out on a place as a faster loser in the final. Scotland's Lynsey Sharp finished second in her 800m heat behind defending Olympic champion Pamela Jelimo, easily qualifying automatically for the semi-finals.