The seven U.S. men in the Wimbledon main draw represent the country's smallest contingent since 1947, when only five played at the grass-court Grand Slam tournament.

Three are scheduled to be in first-round action Tuesday: 31st-seeded Jack Sock, 37th-ranked Sam Querrey, and 77th-ranked Tim Smyczek.

The 22-year-old Sock — who was born in Nebraska, later lived in Kansas City, and now is based in Florida — is seeded at a Grand Slam tournament for the first time in singles. A year ago at the All England Club, he lost in the second round of singles, but he won the men's doubles championship with Vasek Pospisil of Canada.

On Tuesday, Sock will face Sam Groth of Australia, a big server who is ranked 69th, in a rematch of sorts. Sock and Pospisil eliminated Groth and Sergiy Stakhovsky in the first round of doubles on Monday.

Querrey meets 170th-ranked qualifier Igor Sisling of the Netherlands, while Smyczek plays 30th-seeded Fabio Fognini of Italy, a volatile sort who was fined $27,500 last year at Wimbledon for outbursts during a victory.

Three of the four U.S. men who were in action Monday won: 17th-seeded John Isner, 52nd-ranked Steve Johnson and 105th-ranked wild-card entry Denis Kudla, who eliminated 28th-seeded Pablo Cuevas.

Here's what else is happening Tuesday at Wimbledon:

KVITOVA'S DEFENSE

Petra Kvitova opens defense of her title against 108th-ranked Kiki Bertens of the Netherlands on Centre Court. "The pressure, the nerves (are) going to be there, for sure," said Kvitova, who won Wimbledon in 2011. She pulled out of a warmup event at Eastbourne, England, last week, citing a viral illness. The second-seeded Kvitova is 22-6 this season, and one of those victories was more noteworthy than the others: She beat Serena Williams in the semifinals en route to the title at Madrid. It was Williams' only loss in 2015.

GRASS-COURT CHAMPS

With the extra week added to the schedule after the French Open, there were five grass-court tournaments leading up to Wimbledon, and the five men who won those titles play first-round matches Tuesday. That includes past Wimbledon champions Roger Federer, Rafael Nadal and Andy Murray, along with wild-card entry Nicolas Mahut and Denis Istomin. In the Open era of professional tennis, which dates to 1968, only 14 times has the winner of a tuneup tournament gone on to win Wimbledon.

NADAL'S RECENT WOES

From 2006 to 2011, Nadal participated in Wimbledon five times (he skipped 2009 because of a knee injury), and reached the final each time. He lost to Federer in the 2006 and 2007 title matches, beat him in 2008, beat Tomas Berdych in 2010, then lost to Novak Djokovic in 2011. And since? He lost in the second round in 2012, in the first in 2013, and the fourth last year. Seeded 10th this time around, Nadal plays his opening match against 42nd-ranked Thomas Bellucci of Brazil. Nadal has won all four matches, and all 11 sets, they've played in the past against each other.

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