Anita Wlodarczyk and Ruth Jebet both claimed a piece of history inside the Olympic Stadium as they claimed golds in hammer and the 3,000 metre steeplechase respectively.
Wlodarczyk was dominant in the hammer final with a second throw that broke the Olympic record, before going over a metre clear of the previous world record with her next attempt.
The Polish thrower progressed from 80.40 metres to finish the competition on 82.29m, seeing her upgrade her silver at London 2012 to gold in Rio.
Jebet was also celebrating after claiming Bahrain's first gold medal, but she missed out on having a new world record to her name.
In the women's 200m heats all the main contenders booked their places in the semi-finals apart from two-time champion Veronica Campbell-Brown, the Jamaican 27th fastest.
Christian Taylor produced the longest jump in the men's triple jump qualifying round as he leapt 17.24m, the American joined by Dong Bin, Will Claye, Cao Shuo and Nelson Evora in the final.
Kenya's Conseslus Kipruto was fastest in the men's 3,000m steeplechase, but his compatriot - and world champion - Nicholas Bett crashed out in the 400m hurdle heats after clattering a hurdle 30m from the line.
Wlodarczyk set the hammer competition alight as she set a new Olympic record early in the final, but she was not finished as she smashed the world best moments later.
The third throw of Wlodarczyk's final broke new ground as she smashed her own world record by over a metre, the sixth time the 31-year-old has set a new benchmark.
QUOTES OF THE DAY
"I'm happy now. I'm much better. I'm glad it went so well in the 200. I've now got the chance to show what I am capable of doing," Dafne Schippers - who finished fifth in the 100m final - after qualifying for the 200m semi-finals
"I pray I can be part of the Olympic story. There are amazing things happening here and why not me? My goal is the world record. If you come out with that then you get the gold medal," said triple jump heat winner Taylor.
"This is the second time that I missed the world record. I admit that it was easy for me [to achieve], but nobody told me about the record. I wanted the gold medal," Jebet reveals why she did not push for the line in the steeplechase.
The first session of track and field brought plenty of excitement, and the second promises to do the same with David Rudisha, Allyson Felix and Renaud Lavillenie all in action in the 800m, 400m and pole vault respectively.