Novak Djokovic sent out a warning to his rivals at the ATP Finals on Monday, brushing aside big-serving John Isner 6-4 6-3 to launch his bid for a record-equalling sixth ATP Finals title in style.
Earlier, in the same Guga Kuerten group, Alexander Zverev made it six consecutive wins against Marin Cilic in a contest at London's O2 Arena featuring scores of unforced errors.
World number one Djokovic, though, was playing a different game, appearing little troubled by the howitzers coming off the giant Isner's racquet -- breaking his opponent three times and not conceding a single break point on his own serve.
In stark contrast to second seed Roger Federer, who produced an error-strewn performance in defeat to Kei Nishikori on Sunday, Djokovic hit just six unforced errors and won 86 percent of points on his serve, making a mockery of the apparent challenging nature of the playing surface.
"The match was great, obviously," said the 31-year-old. "I had three breaks of serve of John which is sometimes mission impossible but I managed to be at the right place at the right time.
"I held serve well, I backed it up from the baseline, I played very solid and didn't give him many opportunities."
Speaking about the court conditions, he said: "It takes a little bit of time really to get yourself adjusted to the surface... it takes a lot of rotation, takes a lot of spin. When you serve well, also it accelerates through the court."
- Zverev triumphs -
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"The court is difficult," said Zverev. "The court is very fast. And it's very high-bouncing as well. So, it's more difficult than in other tournaments, so everybody has to kind of find their rhythm in the first match. "