By Barry Malone
His opponent, Ethiopian teenager, Jirata Demksa, smiles and prays the Swiss is having an off day.
But Federer just pauses and, taking a deep breath, serves a blistering ace.
The 17-year-old, realizing he's beaten, simply shrugs.
"He's the best tennis player ever," he says. "I am just lucky we played ping-pong."
Jirata says he will never forget taking two points from Federer in an impromptu game of table tennis at a school the tennis ace funds in the poor country.
For Federer, this week's visit to Ethiopia was one that moved him to tears.
"When I arrived at the school and all of the children were singing, it was very emotional," Federer told Reuters.
"They sang, "Roger, our Father' to me. I didn't really understand it at the beginning but I still had tears in my eyes."
"My Mum being from South Africa is obviously the inspiration behind the foundation," Federer said, as local kids screamed "Number one!' behind him.
"I went there on vacation a lot when I was younger. So we started with a project in South Africa and, as I got older and got more money, I wanted to expand."
Eating a lunch of traditional injera -- a sort of spongy pancake -- with the students at one of two schools he pays for in the country, Federer was peppered with questions. Most of the children wanted to know if he had any of his own.
His seven-month old twin girls, Myla and Charlene, could eventually take over the charity Federer wants to continue long after he stops playing, he said.
"I definitely want to show them that this world exists as well," Federer said, gesturing at the tin-roofed classrooms around him.
"There's no way around it for them because I'll be traveling. It will be a very exciting ten years for me because I'll be trying to educate and help them and show them all these things."
Ethiopia is the world's seventh largest recipient of foreign aid, receiving more than $1.94 billion in 2006, according to the Paris-based Organization for Economic Cooperation and Development (OECD).
About 12 million of the Horn of Africa country's people are reliant on foreign food aid to survive.
As multi-millionaire Federer drove through the streets of the capital Addis Ababa, four street kids caught a glimpse of him through the window of his coach.
Leaping to their feet, they ran after the bus.
"Federer! Federer! We love you! We love you!" they shouted.
"It's my first time here so I didn't expect this," he said. "I always think I should have been to a country before people know me. I forget about the television."
Local girl Nihlaa Omar, stretching before racing against the tennis maestro in a 1km fun run, said she had seen him on television in a nearby town.
"We know he's as famous as our famous runners like Kenenisa Bekele," she said referring to the twice Olympic 10,000 meters champion. "But I think Ethiopians can beat him at running."
Federer, who was to run against the school's best athletes, agreed saying: "I'm in a lot of trouble."
The race kicked off, with the Swiss immediately humbled as the Ethiopian children, who live at high altitude, overtook him en masse, a goat leading the field for the first 500 meters. Federer finished near the back of the field.
"I've always had massive respect for long distance sports," he said. "The terrain was so dangerous and they ran barefoot. It was impressive to say the least."
The children, too, were confused by a man more used to split-second exertion.
"How old are you?" one girl said. Super-fit Federer, 28, asked her to guess.
"I don't know about white people," she said, shyly. "45?"
(Editing by Ken Ferris
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