London - Aries Merritt's bid to win the world 110 metres hurdles title two years after undergoing a kidney transplant got off to a smooth start on Sunday.
The 31-year-old American -- whose sister LaToya donated a kidney to him days after he won world bronze in Beijing in 2015 -- cruised through his first round heat at the London Stadium where he won Olympic gold in 2012.
"My whole purpose in life is to inspire others and I hope everyone can take the lesson you can succeed if you put your mind to it," said Merritt after his heat.
However, the world record holder has tough opposition barring his way including the man who succeeded him as Olympic champion Omar McLeod, who is intent on breaking Merritt's world mark.
However, he looked sluggish in his heat before finding enough to come through and win it.
"I was just playing it safe and saving myself for the final. I was just being race smart," he said.
"There is nothing wrong with my fitness. I am ready to go."
Earlier American Kerron Clement opened his campaign for a third world title in the 400m hurdles easing home in 49.64sec but veteran Puerto Rican Javier Culson looked a shadow of the man who won two world silvers and an Olympic bronze finishing sixth in the same heat and failed to go through as a fastest loser.
"I feel in shape but I am not 20 anymore, so I can't run two fast races in a row. I'm ready to peak at the right time and I am fully prepared for a 47 to win," said 31-year-old Clement.
Clement's chances of a third gold were enhanced considerably when the fastest man in the world this year Kyron McMaster of the British Virgin Islands showed his inexperience in major events and was disqualified after finishing second in his heat.
McMaster, 20 and a truck driver in his spare time, was not the only one to fall foul of the race stewards as American Michael Stigler -- second in the national trials -- was also disqualified after initially qualifying in his heat.
American athletics great Allyson Felix cantered home in her opening 400m heat, the 31-year-old defending champion bidding for a 10th world gold.
"I just controlled the race," said Felix.
"I just wanted to feel comfortable to qualify. I feel good, peaking at the right time."
However, standing in her way will be Shaunae Miller-Uibo the Bahamian who denied her Olympic gold last year and who looked in sublime form as she posted a faster time in her heat of 50.97sec.
Veteran Jamaican Novlene Williams-Mills has continued her career remarkably after suffering from breast cancer and undergoing a mastectomy but even at 35 years of age she shows no signs of diminished ability and cruised into the next round.
The men's 3000m steeplechase Rio Olympics silver medalist Evan Jager of the United States topped the times whilst four-time world champion and double Olympic gold medalist Ezekiel Kemboi had to wait to go through as one of the fastest qualifiers.
Jager is not taking anything for granted despite having the fastest time in the world this year and his dominant performance in the heat.
"The final is going to be a hard race," said Jager.
"I am here to try to win gold but all you can do is just to prepare for the best.
"So just because I have the world lead, I do not feel like an overwhelming favourite."
Kenya the traditional powerhouse in the event lost one of its four contenders as 2008 Olympic champion and 2007 world gold medalist Brimin Kipruto failed to qualify.