ATP World Tour Finals - Ferrer upsets struggling Murray
British number one Murray could not get out of second gear throughout the match and lost a fierce baseline encounter in straight sets despite being a break up in both sets of a contest watched by 17,000 fans at the O2 in London.
"I am very happy. I played very consistently throughout the match," said Ferrer. "Andy seemed to have problems with his back, but I played my game and won the match.
"This is only the first match, and I will have to be focused on the next matches in the tournament."
Murray could have few complaints about the nature of his defeat such was his inconsistency.
He needed a medical time-out at the end of the first set for treatment after struggling with what seemed to be a hip or back problem, but was later confirmed as a groin injury. Murray will decide on Tuesday whether the injury is serious enough to prevent him from continuing in the event.
Murray's travails should not detract from an impressive victory for Ferrer, who had lost all five of his previous encounters with the Scot on the same surface. Murray leads 5-4 in their career head-to-heads.
In the final analysis, Murray made 44 unforced errors compared to 35 from Ferrer with the Scotsman nailing 21 winners to 19 from Ferrer as the Spaniard - who lost the final of this tournament to Roger Federer in Shanghai four years ago - saluted a shocked crowd in London after emerging victorious from two hours of unremitting play.
Murray - seeded third this week - will need to come up with wins in his final two Group A games against world number one Novak Djokovic and Tomas Berdych to have a chance of reaching the last four. He is likely to need to win them in straight sets to be sure of progress.
Ferrer made a series of errors in being broken for the first time in the third game only to break back immediately with Murray - toiling for any degree of certainty on his serve - guilty of making three errors on the forehand side as his opponent restored parity at 2-2.
Murray managed to produce a stunning running backhand winner in levelling at 3-3. The match continued on serve until Ferrer produced a fine game to snare the opening set by breaking Murray for a second time in the match.
Murray broke in the opening game of the second set and held for a 2-0 lead only for Ferrer to win three straight games for a 3-2 advantage.
Murray broke for a second time to lead 4-3 after Ferrer threw in a couple of uncharacteristic errors, but could not cement the break as a first double fault of the set helped the Spanish player - who saw a break point elude him to lead 4-2 - draw level at 4-4.
Ferrer finally saw out the match with Murray trying to force the tie-break trailing 5-6.
Ferrer brought up match point at 30-30 by coming to the net to convert a winning volley that bounded beyond Murray, before racing towards the net moments later to thrash the ball beyond the Scot seconds after he had somehow got the ball back over the net with a desperate lunge on the forehand side.