* Del Potro rallies to beat Kohlschreiber
* Berdych, Tsonga register easy victories (Updates after Nadal win)
Oct 9 (Reuters) - Top seed Novak Djokovic launched his Shanghai Open title defence in fine style, breezing past Spain's Marcel Granollers 6-2 6-0 on Wednesday.
Roger Federer, playing his first singles match since a fourth-round exit at the U.S. Open over a month ago, made a brisk return to winning ways, beating Andreas Seppi 6-4 6-3.
The Swiss's long-time rival Rafa Nadal was among those who were eager to see the 17-times grand slam champion in full flight and after observing a few games courtside, the Spaniard showed his own class in a 6-3 6-2 thumping of Alexandr Dolgopolov.
"The court is fast, faster than the previous years," said Nadal, who narrowly missed out on winning his 11th title of 2013 by falling to Djokovic in the Beijing final.
"The serve worked great. Something that didn't happen last week. That's a very important thing."
Djokovic, who lost his world number one ranking to Nadal on Monday, needed treatment on his right foot during the second set of his match but it did not stop him from breaking his opponent three times to win at a canter.
"There's several tournaments left for me, this included, where I will try to go as far as I can... eventually have an opportunity to get back to No. 1 (but) it doesn't depend only (on) me, it depends (on) Nadal," said the Serb, who beat Nadal on Sunday in the China Open for his fourth title of the year.
"Now to build that confidence, try to (be more) aggressive on the court and get my game back to where it should be, that's the primary focus."
Federer, who is drawn to meet Djokovic in the quarter-finals, looked rusty at the start conceding a break in the fifth game against Seppi, who not beaten him in nine meetings.
But the Swiss, who is trying to garner enough points to book his place for next month's ATP World finale in London, got the break back in the next game to level the match at 3-3 and broke the Italian's serve once more to take out the first set.
The second set was far more comfortable for the 17-times grand slam winner, who teamed up with little-known Chinese Zhang Ze for doubles action on Monday, as he held on to an early break without facing any problems on his serve.
DEL POTRO STRUGGLES
Sixth seed Juan Martin del Potro overcame a slow start to beat German Philipp Kohlschreiber 3-6 6-3 7-6(4).
Kohlschreiber, ranked number 23 in the world, served 22 aces and hit 50 winners against a sluggish del Potro. But the Argentine, who said he had been feeling ill, fought back to get an early break in the second set and get a grip on the match.
"It was really tough for me," del Potro, who later withdrew from doubles, told reporters. "I couldn't run a lot. I think my serve helped me a lot to keep playing for the three sets because I made many aces.
"With my serve I didn't run too much. I was lucky in the tie-break because he made a few mistakes. I won a really tough match."
France's Jo-Wilfried Tsonga had a much easier start to his campaign as he brushed aside Pablo Andujar 6-3 6-2 in 65 minutes.
Tomas Berdych of Czech Republic, currently sixth in the race for London, also took a positive step towards sealing his berth by defeating Spain's Feliciano Lopez 7-6(5) 6-2. (Writing by Sudipto Ganguly; editing by Ossian Shine)