RIO DE JANEIRO -- Perhaps it was the 25 mph winds. Or the slower-than-expected hard courts. Or maybe simply that Serena Williams hadnt played a match in a month.Whatever the cause, Williams opened defense of her Olympic singles gold medal with a patchy-at-times 6-4, 6-2 victory over Australias Daria Gavrilova on Sunday, gesturing or yelling at herself as she often does when not all goes her way.Im always frustrated on the court if its not perfect, the American said.Williams had not competed since collecting her Open-era record-tying 22nd Grand Slam title at Wimbledon. Shes now won 19 of her past 20 matches.Seeded No. 1 at the Rio de Janeiro Games, Williams was hardly at her best in the 91-minute contest against Gavrilova, who is ranked 46th and only once has been past the second round at a major tournament.While that match was played in the main stadium, action was delayed because of strong winds for about 2 hours on the eight smaller Olympic courts.I was a little nervous about that, Williams said of her reaction to hearing of the gusty conditions, which she called very intense.Williams compiled 37 unforced errors to 27 winners, and got broken at love while serving for the first set at 5-3, a game that included a tremendously entertaining point.The lengthy exchange featured terrific defense by both women and ended with Williams putting a forehand into the net. Afterward, she leaned over near the net, while Gavrilova dropped to her knees on the court, letting go of her racket.But Williams broke right back in the next game to take the set.The first set, especially, was extremely tricky, Williams said, referring to the wind, but Im glad it kind of slowed down in the second a little bit, so I was able to produce better tennis.Players have noticed that the green courts in Rio play slower and offer higher bounces than hard courts used on the North American circuit leading to the U.S. Open later this month.Fortunately enough, I am a pretty good clay-court player, so Im OK with the slow courts, said Williams, a three-time French Open champion. You have to hit about three or four more shots or just play a little bit better. Its OK. Im getting used to the conditions as a whole.Later Sunday, Williams and her older sister Venus lost an Olympic doubles match for the first time. They are three-time gold medalists as a team, and entered this match with a 15-0 record at the Olympics, but were beaten 6-3, 6-4 by the Czech Republics Lucie Safarova and Barbora Strycova.On Saturday night, Venus availability for doubles was put in doubt by U.S. womens tennis coach Mary Joe Fernandez, who said the four-time gold medalist and seven-time Grand Slam champion had cramping, dehydration and an upset stomach following a first-round loss in singles.---Follow Howard Fendrich on Twitter at http://twitter.com/HowardFendrichVans Old Skool Clearance . Zvonareva, who won the tournament in 2009 and 10, couldnt handle her opponents big groundstrokes in only her third event back after 17 months out with a shoulder injury. Zvonareva made her comeback in January in Shenzhen and played in the Australian Open but lost her first matches at both tournaments. Vans Old Skool Cheap Online . However, he did make them miss him a little less. Cundiff, who had the unenviable job of replacing Dawson last season, agreed Thursday to a one-year, $1. http://www.cheapoldskool.us/ . Third-seeded Murray had the easiest path to victory on New Years Eve, barely breaking a sweat during his 6-0, 6-0 win over 2,129th-ranked Qatari wildcard recipient Mousa Shanan Zayed. Vans Old Skool Sale Cheap . -- Linebacker Myles Jack ran for four touchdowns, defensive end Cassius Marsh caught a scoring pass, and No. Cheap Old Skool Wholesale . "Four now," Carl Gunnarsson told the Leaf Report proudly following a 5-2 victory over New York on Tuesday night, the clubs fifth straight at home.Real Madrid have remained the most valuable football team in the world for a fourth year in a row. The Spanish giants lead the way from rivals Barcelona, with Manchester United sitting in third place. Balagues La Liga best XI Sky Sports Spanish expert Guillem Balague has picked his best XI from La Liga in the 2015/16 season According to US business magazine Forbes, Real Madrids value stands at 3.645bn US dollars (£2.52bn) and their annual revenue is $694m (£480million), a slender advantage over Barcelona in both categories. Barcelona are shown by rich list to have a value of $3.549bn (£2.46billion), with United said to be worth $3.317bn (£2.3billion).Six Premier League teams feature in the top 10, with United joined by Arsenal, Manchester City, Chelsea, Liverpool and Tottenham. As Atletico and Real Madrid get set to meet again in the Champions League final, we look back at the past meetings between the sides Forbes said the top 20 teams are collectively worth 24 per cent more than the teams that filled those positions 12 months ago, citing increased income from television contracts and kit deals.ddddddddddddThe study said Real Madrid ranked as the worlds second richest sports team, behind only the Dallas Cowboys American football team which it valued at four billion dollars (£2.77bn).Forbes top 10 worlds most valuable football teams:1 Real Madrid - US$3.645 bn (£2.52billion)2 Barcelona - $3.549bn (£2.46bn)3 Manchester United - $3.317bn (£2.3bn)4 Bayern Munich - $2.678bn (£1.85bn)5 Arsenal - $2.017bn (£1.4bn)6 Manchester City - $1.921bn (£1.33bn)7 Chelsea - $1.661bn (£1.15bn)8 Liverpool - $1.548bn (£1.07bn)9 Juventus - $1.299bn (£900million)10 Tottenham - $1.017bn (£704m) Also See: VOTE: La Liga goal of season La Liga final day on Sky Casillas takes swipe at Madrid Live on Sky ' ' '