Venus Williams defeated Italy's Francesca Schiavone 6-3, 1-6, 6-2 and John Isner came from a set down once again to beat Colombia's Santiago Giraldo 1-6, 7-6 (8-6), 6-2 but, oh dear, Serena spoiled the party by losing to an ailing but determined Nadia Petrova 6-4, 2-6, 6-3.

Petrova needed to be stretched at changeovers to ease her back but it was Serena who seemed a step slow when it mattered.

"I was definitely not at my best," she admitted. "When you play matches it's totally different from practice. Getting that match play, you put your body under different levels of stress. So hopefully, in a week and a half I will be better for Paris."

Rather than dwell on her defeat, Serena opted to accentuate the positive following her sister's win which, like her match, had been scheduled for Court Three.

"We can definitely celebrate," she said. "I think it's a great feat to be No. 1 and No. 2. It's so amazing. I'm just excited to be ... to be alive!"

The laugh was genuine, but earlier Venus, the more studious and serious of the two sisters, had issued a little warning: "Being No. 1 and No. 2 was what we dreamed of as kids," she said. "I congratulate Serena on that ranking but I am aiming to get there myself."

Isner could take great credit from his win against an opponent who will be lining up in Colombia's Davis Cup colors when the two teams meet in July. It was a chilly and generally miserable day in Madrid and at a set down and 5-5 in the second, the American was giving every indication of wishing he was somewhere else.

The Colombian is ranked only No. 59 in the world but he has been in good form of late and was handling Isner's massive serve with dexterity. Keeping the ball in play on a windy day was of paramount importance and, not surprisingly for a born clay-courter, Giraldo was proving to be better at that. But after serving his way out of trouble in the penultimate game, Isner went into the tiebreak in a determined frame of mind.

"I just told myself whoever won the breaker was going to win the match," he said after coming off court later in the day with a doubles win under his belt. "The ball was swirling around and it was probably a match I could have lost. He was playing well but I dug deep and got through it."

Despite netting a volley to hand back a mini-break on serve, Isner eventually got control of the tiebreak to win it 8-6 and then his serve took over in the third set as Giraldo tired.

Later Isner was back in harness with his pal Sam Querrey and this increasingly effective doubles partnership also fought back from a first set loss to beat the Brazilian pair of Thomaz Bellucci and Bruno Soares 2-6, 7-5, 1-0 (TB) .

"Sam and I are pretty laid back which helps us in those situations," said Isner. "After losing the first set we just said 'Let's go for it' and it worked."

Rafael Nadal kept his vocal fans happy with a 6-4, 6-3 win over Alexandr Dolgopolov of the Ukraine while Andy Murray appeared to be in great touch as he swept past the Argentine veteran Juan Ignacio Chela 6-3, 6-3.