Shaunae Miller of Bahamas in action in Barcelona (Alberto Montenegro) © Copyright
Medvedeva the World leader and a hot favourite for the title, sealed victory when making a timely break 50m before the bell in the 1992 Olympic Stadium before motoring around the final circuit and finish in a time of 45:41.74.
Her well-timed assault saw her break clear of her stocky team-mate Leontyeva who nevertheless gallantly chased her to the finish line and was rewarded with a personal best of 45:43.64.
Sandra Arenas the 2012 World Road Race Walking Cup champion in Saransk but not matching that form, followed hot on her heels to capture the bronze medal for Colombia in a time of 45:44.46.
Medvedeva who hails from the Russian city and coped extremely well despite the 25 degrees temperature and humidity of 78%, said: "It was terribly hot, so I am even happier that I have won. I am from Saransk, that as you know is the Mecca of walking.”
The 18-year-old who finished out of the medals at the WRRWC, added: "Walking is now my life. I only started three years ago. I was disappointed that I was only fourth in the World Cup in Saransk. But now I believe in myself."
Leontyeva who recovered after one of her feet was trod on early in the race, said: "It was really, very, very hot but the fans supported me. I am from Cheboksary where walking is very popular.
"After the race I phoned my mum - she was crying. I guess when I go home there will be a big party."
British Girls lead qualifiers for 800m finals
The women's 800m is shaping up to be very close affair after three high quality semi-finals were won by Ukraine's Anastasiya Tkachuk and the British pair of Emily Dudgeon and Jessica Judd.
Tkachuk the World Number 2, eased ahead 50m from the line to win in 2:02.50 ahead of Morocco's Manal El Bahraoui and Anita Hinriksdottir, but the Icelander who had led for most of the two laps, found an extra breath to breeze into second and again lower her National record to 2:03.15.
Great Britain's Dudgeon took her race by the scruff of the neck at the bell and foraging hard she maintained her form to lower her PB by over second with a mark of 2:02.32. Just 0.11 behind her Ajee Wilson wasn't breathing hard as she ran a lifetime best of 2:02.61.
Judd with a very determined last lap claimed the fastest time of the day of 2:02.30 and the effortless way she achieved it ahead of Winnie Nanyondo - the Ugandan claimed a PB 2:02.38 - suggests Elena Lavric's four-year-old Championships record of 2:00.06, will be target in the final.
First round Championships record for Gill
Defending gold medallist Jacko Gill wasted no time in demonstrating why he is the best shot putter in his age group when setting a new Championships record with his opening attempt of 21.50m.
The distance which only himself with his previous World leader of 22.30m set during the Oceania summer in March has bettered this year, smashed the previous record of 21.47m which Croatia's Edis Elkasevic posted in Kingston a decade ago.
Now it is forecast the New Zealander who is defending the title he won as the youngest ever male junior champion in Moncton two years ago, could seriously challenge the World record in tonight's final.
That currently belongs to Germany's current World senior champion David Storl who threw 22.73m in July 2009 and who preceded Gill as World junior title holder with his victory four years ago in Bydgoszcz.
Another Oceania athlete Damien Birkinhead had the second best throw of 20.01m while behind him Mesud Pezer raised the Bosnia Herzegovina record to 19.96 as eight athletes made the automatic qualifying mark of 19.30m.
Other qualification rounds...
The women's Triple Jump final tomorrow looks set to be a closely fought contest between the three top ranked athletes, Liuba M. Zaldivar, Dovile Dzindzaletaite and China's Mudan Chen - although the latter had a bad day at the office in the qualifying round.
Dzindzaletaite of Lithuania produced the best effort of the morning, winging her second leap to 13.85m which would have been a PB except for an over the limit following wind of 2.7m/s, while Cuba's Zaldivar cleared 13.80m - only 11cm shy of her World lead - with her opening attempt.
While they thrived in the morning sunshine, an off colour Chen who like Dzindzaletaite has cleared 13.72m this year, managed a best jump of only 13.01m which ranked her 11th qualifier.
World leader Ashley Spencer strongly backed to become the first USA 400m gold medallist since Natasha Hastings triumph in Grossetto eight years ago, was fastest in the qualifying rounds where five other contenders went under 53 seconds.
Spencer who decided to concentrate on the WJC than chase a Team USA Olympic place, led the way with a very easy looking run of 52.58 with defending champion Shaunae Miller also looking in great shape.
Miller who after her win in Moncton "stepped down" and went on to capture the World Championships Youth crown in Lille last summer sauntered to a time of 52.71, while the third fastest Patrycja Wyciszkiewicz set a Polish record of 52.76.
World leader Felix Franz ran well within himself where the seven 400m Hurdles heats saw plenty of athletes clattering the hurdles and South Africa's Bernardus Pretorius falling flat on his face after mistiming the ninth in his race.
Franz who is World leader with the time of 50.48 took no chances and ran simply to qualify for the semi-finals which he did without incident when third in his heat recording a 51.78.
The German will be very wary of American Greg Coleman who still seemed to have plenty in reserve when clocking the fastest time of the day of 50.95. "I am happy from my new PB and I hope to improve it in the semi-final," he said.
Slovenia's Mitja Lindic followed him with his fastest ever time of 51.16 and Japan's Takahiro Matsumoto ran a very easy looking 51.26.
Three points separate top 2 in men's Decathlon after 5 events
The Decathlon continued to see the lead switch and after winning the 110m Hurdles Tim Dekker was the fifth and latest gold medal contender to go to the top of the leaderboard.
The Dutchman trailing overnight leader Gunnar Nixon by just 10 points clocked 14.02 for a decisive win ahead of his USA opponent who recorded 14.54.
That saw the main contenders Dekker on 5126 points, Nixon having a total of 5070pts and the Australian duo Dubler and Stein who recorded 14.62 and 14.90, having tallies of 4997pts and 4963pts.
Following the discus Dekker was hanging on to the lead by the skin of his teeth. Despite a PB throw of 43.69m and an aggregate of 5866pts he was only three points ahead of Stein a throwing specialist who winged his implement a distance of 51.43m.
Nixon after a PB of 42.23m dropped to third tallying 5780, Pieter Braun of the Netherlands thanks to his best ever effort of 44.24m moving fourth with 5675pts, while Dubler who only managed 36.15m dropped to fifth (5584pts).
David Martin for the IAAF