Kevin Mayer assumed the early lead in the decathlon after the morning session at the IAAF World Championships and Kendra Harrison made an ominous start to her quest to be crowned 100 metres hurdles champion.
Mayer is the favourite to take gold at London Stadium in the first major competition since Ashton Eaton's retirement and the Frenchman lived up to his billing in the first three events on Friday.
The Olympic silver medallist picked up 2703 points, opening up an advantage of 325 points from Germany's Rico Freimuth.
Trey Hardee of the United States is a further 31 points behind the early frontrunner following the 100m, long jump and shot put, with the high jump and 400m to come later in the day.
Harrison set the world record in London last year and laid down a marker in the heats on the same track, setting the pace with a time of 12.60 seconds.
Deborah John of Trinidad and Tobago was carried off following lengthy treatment after suffering a horrific fall in the fifth heat.
MAYBE THE SIGN OF THINGS TO COME?
Mayer took silver in the Rio Olympics last year, but with Eaton out of the picture the time may have come for the 25-year-old to strike gold.
Not renowned for his sprinting, Mayer started with a personal best of 10.70secs in the 100m, with Damian Warner fastest in a time of 10.50secs.
Mayer followed that up with a season's best of 7.52m in the long jump, Freimuth taking over the lead with a leap of 7.48m as Warner managed 7.44m.
Another season's best of 15.72m in the shot put ensured it is Mayer who is the man to catch.
HARRISON SHOWS LIKING FOR LONDON
Harrison put the misery of missing out on Olympic qualification behind her in emphatic fashion by shattering the world record in the Anniversary Games last July.
There could be something special to come from the American in London again just over 12 months on after an encouraging start in the heats.
Defending champion Danielle Williams was second quickest, winning heat one in 12.66secs. Megan Simmonds, Sally Pearson and Christina Manning also won their heats.
The morning track action ended on a sour note with the sight of John being taken away after crashing down in the final race.
John appeared to injure herself before clattering head first into the fifth hurdle and hitting the deck hard.
KYNARD OUT OF HIGH JUMP
The United States lead the way in the medals table, but Erik Kynard will not be adding to their haul in the high jump.
Olympic silver medallist Kynard withdrew due to injury after failing to clear 2.17m in his first attempt in the qualifying competition.
Strong favourite Mutaz Essa Barshim of Qatar was among the six men to move into Sunday's final by going over the automatic qualifying height of 2.31m.