* Djokovic's Serbia lead Belgium 2-0 in Charleroi
* Holders Czech Republic level with Switzerland
* Germany's Kohlschreiber retires hurt v Argentina
Novak Djokovic quickly got back in the groove after his Australian Open triumph with a crushing defeat of Olivier Rochus as Serbia surged into a 2-0 lead in their Davis Cup world group, first round tie in Belgium on Friday.
Holders Czech Republic were locked at 1-1 after the first day against a Switzerland side minus world number two Roger Federer - Tomas Berdych levelling the tie after Lukas Rosol had been outplayed by Stanislas Wawrinka.
Germany's hopes of beating Argentina in Buenos Aires suffered a cruel blow, however, as Philipp Kohlschreiber was forced to retire with a hamstring injury when serving for the match at 5-4 in the fifth set against Carlos Berlocq.
A later win for Juan Monaco over Florian Mayer meant Argentina ended the day 2-0 ahead as did France and Kazakhstan in their ties against Israel and Austria respectively. Top seeds Spain were in action later against Canada in Vancouver.
Less than a week after claiming a third consecutive Australian Open title by beating Andy Murray in Melbourne, world number one Djokovic quickly adapted to the indoor clay court at the Spiroudome in Charleroi to blow away Rochus 6-3 6-2 6-2.
Serbia's Viktor Troicki, playing in place of the absent Janko Tipsarevic, battled back from two sets down to beat David Goffin in the opening rubber.
Troicki, who won the deciding rubber when Serbia beat France to win the Davis Cup for the first time in 2010, produced a gutsy display after being outplayed for two sets.
Friday's match began to spin away from Goffin in the third set as Troicki clawed his way back to win 1-6 3-6 7-6 6-4 6-4.
On the eve of the match, Serbia had criticised the playing surface, saying the decision to lay a clay court on top of a wooden floor was dangerous.
The International Tennis Federation (ITF) issued a statement saying they were happy with the court and it seemed fine for Djokovic who fired down 20 aces in a one hour 39 minute breeze.
"The serve was incredible and I think that helped me to get the match done in straight sets which was important," Djokovic said. "It wasn't easy playing on clay after a long time indoors and coming from Australia quite late.
"At the start I had trouble with movement and getting used to the conditions but I played my best tennis when I needed to."
A strong France lineup had too much for visitors Israel on the opening day in Rouen where Jo-Wilfried Tsonga needed four sets to beat Amir Weintraub before Richard Gasquet made short work of Dudi Sela.
"It is the perfect scenario because we've got two wins under our belt," team captain Arnaud Clement told reporters. "We will need to be very focused so we can wrap this up tomorrow."
In other ties, Croatia and Italy were locked at 1-1 in Turin while the United States, who have won the competition a record 32 times, edged ahead against Brazil in Jacksonville after Sam Querrey dispatched Thomaz Bellucci in straight sets.