The Serbian star Djokovic (1-0) staved off a match point before outlasting the seventh-seeded Czech slugger Berdych in 3-6, 6-3, 7-6 (7-3) fashion. Berdych (0-1) had a match point at 6-5, 40-30 in the third set, but netted a forehand to give Djokovic life.
Berdych broke Djokovic to grab a 4-2 lead in the final stanza, but the Serbian sensation broke right back to deflate the big Czech.
Djokovic commanded the match-deciding tiebreak and converted on his first match point when Berdych netted one final return after 2 hours, 39 minutes of tennis.
The amazing Djokovic improved to 70-4 in 2011.
The reigning U.S. Open, Wimbledon and Aussie Open champion Djokovic, who captured this prestigious season-ending tournament back in 2008, owns a tour- best 10 titles on the circuit this season.
Meanwhile, a fifth-seeded Ferrer surprised the world No. 3 Murray 6-4, 7-5 on the indoor hardcourt at The O2 arena in London.
Ferrer rallied from a break down in the second set to prevail in exactly two hours, as he broke Murray on five occasions, compared to three breaks for the three-time Grand Slam runner-up from Scotland.
The 2007 Tour Finals runner-up Ferrer is 1-0 in the four-player Group A, while the 2011 Australian Open runner-up Murray is 0-1.
Murray, who required a medical timeout to receive treatment for a groin injury between sets on Day 2, wound up with a whopping 44 unforced errors. He will decide on Tuesday if he can stay in the tournament this week.
The 29-year-old Ferrer is now 6-8 this year against top-10 opponents.
This exclusive event features only the top-eight players in the world. The four-player Group B is comprised of second-seeded Rafael Nadal (1-0), fourth- seeded Roger Federer (1-0), sixth-seeded Jo-Wilfried Tsonga (0-1) and eighth- seeded American Mardy Fish (0-1). The five-time Tour Finals titlist Federer defeated his great rival and fellow former No. 1 Nadal in last year's finale in London.
Nadal and Federer will lock horns at The O2 on Tuesday. The mighty Spaniard topped the Swiss icon in this year's French Open final.
The 16-time Grand Slam champion Federer has been the hottest player of late, as he entered this event with a 12-match winning streak. He beat Tsonga for the Paris Masters crown two weeks ago and titled in his native Basel the week before that.
Also on Tuesday, the former Aussie Open runner-up Tsonga will take on Fish.
Round-robin play will be staged through Friday in London, while the semifinals will be held on Saturday and the lucrative final will be played Sunday. The top-two finishers from each group will compete in the semis.
This week's big winner will earn at least $770,000. An undefeated champion would pocket $1.63 million.
In some round-robin doubles action on Monday, the world No. 1 twin Bryan brothers, Bob and Mike, came from behind to sneak past the seventh- seeded duo of Austrian Jurgen Melzer and German Philipp Petzschner in three sets, 6-7 (4-7), 7-5, 10-7. The American Bryans, who saved a match point on Monday, were this year's Wimbledon and Australian Open champs, while Melzer and Petzschner captured the U.S. Open.