The elections reflected the improved standing of the U.S. in the International Olympic Committee after years of strained relations, and gave further impetus to a potential American bid for the 2024 Summer Games.
"Having another member in the Olympic family, in the IOC, and having Anita on the executive board, I think it's a big deal and it's good news for the USOC and the United States," Probst said.
Probst was elected by a vote of 71-20, becoming the fourth U.S. member on the Swiss-based body. The chairman of video game publisher Electronic Arts Inc. joins DeFrantz, Jim Easton and Angela Ruggiero as IOC delegates.
Probst is the first U.S. Olympic Committee president to hold IOC membership since Sandra Baldwin, who resigned from both posts in 2002 after admitting to having lied about her academic credentials.
Perhaps even more significant than Probst's election was DeFrantz's victory in a three-person race for a spot on the policy-making executive board. The U.S. has been without a voice on the board since Easton lost his seat in February 2006.
DeFrantz won by a single vote — 41-40 — against senior Canadian member Dick Pound. Malaysia's Prince Tunku Imran was eliminated in the first round.
DeFrantz and Pound are former IOC vice-presidents. Both also lost to Jacques Rogge in the 2001 IOC presidential election.
DeFrantz, chair of the women and sports commission, had lost previous bids to return to the executive board.
"That's a terrific thing for the USOC to have some representation on the executive board. It's been a while," Probst said. "As an IOC member, I'm very excited about that."
The votes took place before the election of Germany's Thomas Bach as the new IOC president, succeeding Rogge.
Without a voice at the top IOC table and holding few top jobs in international sports, the U.S. had lost considerable clout over the years in Olympic circles — underlined by New York's defeat in the race for the 2012 Olympics and Chicago's first-round elimination in the vote for the 2016 Games.
Under Probst and CEO Scott Blackmun, the USOC has made significant strides in mending fences with the IOC and establishing an international presence. Last year, the USOC and IOC resolved a long-standing dispute over Olympic revenues that had kept the American body alienated from the rest of the world.
Probst's election comes as the USOC weighs a possible bid for the 2024 Summer Games. The U.S. hasn't hosted a Summer Games since 1996 in Atlanta or the Winter Games since 2002 in Salt Lake City. Several U.S. cities have expressed interest in trying to 2024.
Bach said it was a good time for the U.S. to bid.
"We appreciate his enthusiasm ... but that's something we've got to be very thoughtful about," Probst said. "Ultimately our board will decide if we will move forward with the bid. ... The first step is we have to decide that we are going to move forward and we have to go through a process of which city gives us the best chance."
In another election for a high-ranking position Tuesday, Australian John Coates moved up to become a vice-president. He was the only candidate.
Russian Olympic Committee President Alexander Zhukov also was among the nine candidates elected to the IOC on the final day of its general assembly in Buenos Aires.
Zhukov made it by a vote of 63-29, with two abstentions. The 29 votes against was the most received by the nine candidates, a possible sign of Russia's contentious relations with the West.
Among the other new members are former Olympic high jump champion Stefan Holm of Sweden and Kenyan distance running great Paul Tergat.
With Tuesday's elections, the IOC now has 112 members. The U.S. and Russia now both have four members. Britain also has four while Switzerland has the most with five.
Also elected Tuesday: KLM executive Camiel Eurlings of the Netherlands, Mikaela Maria Antonia Cojuangco-Jaworski of the Philippines, Bernard Rajzman of Brazil, Octavian Morariu of Romania and Dagmawit Girmay Berhane of Ethiopia.
Eurlings replaces King Willem-Alexander of the Netherlands, who resigned his IOC position after acceding to the Dutch throne in April.
"Those are extremely big shoes to fill, I can assure you," Eurlings said. "But what gives me some comfort is that the king ... said that an honorary member can also be very active, so I know that he has a big sports heart and I'm sure that his sports heart will keep on beating."
AP Sports Writer Tales Azzoni contributed to this report.
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