* Serena avenges Venus's defeat by beating Robson
* Djokovic back on track with easy win over Montanes
* Wozniacki, Ivanovic both fall at first hurdle
* Poland's number four seed Radwanska also out (Adds quotes)
May 14 (Reuters) - World number one Serena Williams inflicted swift revenge on behalf of her older sister when she beat Britain's Laura Robson 6-2 6-2 in the Rome Masters on Tuesday.
Venus Williams was despatched in straight sets by Robson in Monday's first round but Serena, fresh from her defeat of Maria Sharapova in the Madrid Open final at the weekend, was a different proposition once she had warmed up.
Robson broke serve in the opening game but the American quickly hit her stride to take the first set. Robson battled hard early in the second to reach 2-2 but then folded in the face of Williams' power and placement.
Robson's second service was picked apart by Williams and the Briton did her chances no good with eight double faults.
"It was a good match - she played really well and really smart," said Wiliams. "She's just a great player and I think she has such a big future...
"I've played lots of matches, but I'm the kind of player who likes to keep playing matches, at least now in my career," Williams said of her current 20-match winning streak. "I just want to keep the confidence there."
Despite being handed a tennis lesson, 19-year-old Robson said she wanted to play Williams again soon.
"She's number one in the world for a reason. She played really well today (and) didn't give me many opportunities," Robson said on the official Tour website (www.wtatennis.com).
"I thought it could have been a little bit closer - I had some break points I didn't take advantage of - but it was a learning experience and hopefully I'll play her again soon."
Novak Djokovic, the men's world number one, bounced back from last week's shock defeat in Madrid to ease past Albert Montanes 6-2 6-3 in the second round.
Djokovic lost in three sets to Grigor Dimitrov at the same stage on the Madrid clay but a repeat was not on the cards in Rome once the Serb recovered from losing an early service game.
Second seed Roger Federer, who failed to get past the third round in Madrid, also hit the ground running against Italy's Potito Starace and closed out a 6-1 6-2 win in 51 minutes.
From 2-1 down, Djokovic took the first set without losing another game and broke the Spaniard early in the second.
"This win means a lot to me because I didn't have a great week in Madrid. I didn't play much, I didn't practise much," said Djokovic, who is already planning for the French Open and Wimbledon.
"I worked very hard to prepare for this tournament. I need to be emotionally and physically fit and I think I'm heading in the right direction."
Federer, beaten by Djokovic in last year's Rome semi-finals, was at his smoothest against Starace and showed no ill-effects from his shock defeat by Japan's Kei Nishikori last week.
"I was not very happy with my performance in Madrid and I had no choice but to hit the practice courts," said the Swiss who honed his serve-volley game against his Italian opponent.
Djokovic and Montanes followed Dimitrov on court in Rome after the Bulgarian's 6-4 6-4 defeat by ninth seed Richard Gasquet of France.
South Africa's Kevin Anderson removed Marin Cilic, the 11th seed, 6-3 7-6 also in the second round while 12th seed Nicolas Almagro and Tommy Haas (13) went out in opening-round matches.
Also in the women's draw Caroline Wozniacki, seeded 10, and 15th seed Ana Ivanovic failed to clear the first round.
Wozniacki led 4-0 in the third set against Bojana Jovanovski and served for the match at 5-4 but her Serbian opponent, who had lost her last eight matches before this, fought back to claim the second top-10 scalp of her career.
Fourth seed Agnieszka Radwanska of Poland took the first set in her second-round match with Romania's Simona Halep but won just three games in the next two to go down 6-7 6-1 6-2. Her sister, Urszula, had a better day, beating Ivanovic 6-3 2-6 6-2. (Writing by Robert Woodward in London, editing by Pritha Sarkar and Ken Ferris)