Spanish walker Martin wins first gold of Budapest worlds
The two-time European champion clocked 1hr 17min 32sec for the victory on the streets of the Hungarian capital in a fast race that saw five of the first six finishers break national records.
"I was fourth at the last Olympic Games, I missed the bronze which motivated me to work hard," Martin said.
"In Tokyo, I felt when I was in the fourth position that I could win a medal. Unfortunately, it did not happen and that is why this gold medal is next step towards the next Olympic Games" in Paris next year.
The race walk was delayed for two hours because of a heavy storm and the opening day's action at the National Athletics Centre was put back an hour.
Sifan Hassan kicked off her audacious bid for a world treble by safely negotiating the opening round of the 1500m.
The Dutch runner completed an unprecedented triple at the Tokyo Olympics by winning gold medals in both the 5,000m and 10,000m and a bronze in the 1500m.
She is down to race all three once again in Budapest and will be back in action in the final of the 10,000m later Saturday.
'Keep fighting'
Also safely through into Sunday's 1500m semi-final (with the final on Tuesday) was Faith Kipyegon, who has enjoyed a stunning season in which she has set three world records.
The Kenyan is also entered in the 5,000m, with qualifiers over that distance to be raced on Wednesday and the final set for the penultimate day of action on August 26.
Reigning world shot put champion Ryan Crouser, suffering with blood clots in his lower leg, also sailed through qualification, going out to 21.48m on his first attempt.
"The last 20 days have been some of the most frustrating and stressful of my life," he said on Instagram.
The final of the shot put will be held at 1835GMT.
The fancied Polish duo of Pawel Fajdek and Wojciech Nowicki moved into the final of the men's hammer throw.
Fajdek is seeking a sixth successive world gold that would see him match the record number of titles won in a single event achieved by Sergey Bubka in the pole vault between 1983-97.
But it is Olympic champion Nowicki who is the clear world No.1 in the event at the moment.
With double Olympic champion Nafissatou Thiam of Belgium out injured and unable to defend her title, American Anna Hall took charge of the heptathlon after the opening two events, the 100m hurdles and high jump.
Hall clocked 12.97sec in the hurdles and registered a best of 1.83 in the high jump for a total of 2,145 points.
US teammates Talyah Brooks (2,136) and Chari Hawkins (2,134) were hot on her tail, with Britain's 2019 world champion Katarina Johnson-Thompson in fourth (2,104).
"The high jump didn't end up as I'd hoped but at this type of event you always have to deal with some kind of adversity," said Hall, a world bronze medallist in Eugene last year.
"All I can do is keep fighting and come back to the other events. That's what I'm gong to do. I'm looking forward to the rest of the competition."
The heptathlon continues with the shot put and 200m in the evening session before the long jump, javelin and event-ending 800m on Sunday.