* Djokovic beats Stepanek
* Berdych hits back for Czechs
* Djokovic pondering doubles
BELGRADE, Nov 15 - Roared on by 17,000 partisan fans Novak Djokovic fired Serbia ahead in the Davis Cup final on Friday but Tomas Berdych hit back for the Czech Republic to leave the tie delicately poised going into the weekend.
The opening day went exactly according to the script with home talisman Djokovic seeing off the challenge of Radek Stepanek 7-5 6-1 6-4 in the Kombank Arena just days after winning the ATP World Tour Finals in London.
Berdych was rock-solid as he cooled the atmosphere in the cavernous indoor arena, beating gutsy world number 117 Dusan Lajovic 6-3 6-4 6-3.
Lajovic, a last-minute replacement for the injured Janko Tipsarevic, won the hearts of the home fans with some gritty resistance but could find no way through against the hard-hitting Berdych.
Saturday's doubles, which is likely to feature Berdych and Djokovic, now looks crucial to the outcome of the tie.
"We have not yet decided who will play the doubles tomorrow but if everything stays as it is, Radek (Stepanek) and I are ready to team up because we both feel good and not too exhausted after today's singles," Berdych said.
With Serbia short of injured Tipsarevic and Viktor Troicki, who is serving a doping ban, Djokovic looks like being in for an exhausting end to his season too.
"I am still not sure if I will play in the doubles (on Saturday) because we have to look at Sunday's reverse singles too and the overall exertions of the three-day schedule," Djokovic said after brushing Stepanek aside.
"If selected I will ignore my exhaustion because a full house on a home court brings the out best in me.
"I am not a doubles specialist of course but it's not like I've never played doubles and it also wouldn't be the first time I've been involved in all three Davis Cup days.
"You don't get a chance to play in the final on home court every year so the motivation is huge and I will always be happy to find a way to overcome fatigue after a long season."
Djokovic, who outplayed Nadal in London on Monday, had to work hard to take the opening set after allowing Stepanek to win three games in a row and level at 5-5.
However, he stepped up a gear to see off the battling Czech to give Serbia the perfect start as they seek to repeat their 2010 victory in the final against France.
"The first set was crucial and after enduring a few poor games I came up with some big serves at crucial moments, especially when I faced break points," Djokovic told a news conference in the same imposing Kombank Arena that staged their momentous triumph three years ago.
"After that I felt pretty much in control of the match."
Stepanek squandered an opportunity to break Djokovic early in the second set and was brushed aside after that as the Serb tormented him with stinging baseline power and trademark winners down the line.
Lajovic delighted the home fans with sporadic moments of inspiration against Berdych, especially with his one-handed backhand down the line.
Five times he had Berdych at 0-30 on his serve only to watch powerless as the world number seven took the next four points to snuff out any danger of a shock.
The colourful band of several hundred Czech supporters celebrated with their noisy trumpets as Berdych closed in on victory. One break was all Berdych needed in the first two sets but he broke twice in the third to see off the 23-year-old.
"It was tough because I played a guy I had never seen before and he had nothing to lose," Berdych said.
"It was a difficult situation to handle mentally because Serbia were 1-0 up and he had the backing of the home crowd."
Djokovic is expected to play with Nenad Zimonjic on Saturday. The Czechs have slightly more options with world No.47 Lukas Rosol or Jan Hajek also available to partner either Stepanek or Berdych. (Editing by Martyn Herman)