* Haas ends Djokovic's 14-match winning streak at tournament
* Opens door for Murray to replace Federer as world number two
* Serena Williams moves into semi-finals (Adds details, quotes)
March 26 (Reuters) - Germany's Tommy Haas recorded the upset of the tournament when he stunned two-time defending champion Novak Djokovic 6-2 6-4 in the fourth round of the Sony Open at Miami on Tuesday.
Haas, who turns 35 next week, needed just 80 minutes to end Djokovic's 14-match winning streak at the tournament and consign the world number one Serb to just his second loss of the season.
"Playing against someone like Novak and coming out on top at this time of my career, it's unbelievable," Haas told reporters.
"These are the moments I appreciate the most, going on those big stadiums, big stages, playing against the best people in the world."
Haas's win was his second over a world number one, some 14 years after felling Andre Agassi in the quarter-finals of the 1999 Grand Slam Cup.
"All the credit to him. He played a great match and he was the better player, no question about it," said Djokovic, who won a third successive Australian Open title in January.
"As far as I'm concerned, it's definitely the worst match I have played in a long time."
The victory carried Haas into his first quarter-final at Miami while improving his head-to-head record against Djokovic to 3-4.
The German next plays Gilles Simon after the 11th-seeded Frenchman rallied past another Serbian in Janko Tipsarevic, 5-7 6-2 6-2.
Djokovic's defeat opens the door for second seed Andy Murray, who eased into the last eight with a 6-2 6-4 win over Italy's Andreas Seppi, to replace Roger Federer as world number two should he win the Miami title.
Third seed David Ferrer also cruised into the quarters with a 6-4 6-2 win over Kei Nishikori.
In the women's tournament, Serena Williams continued her bid for a sixth Sony Open title with a hard-fought 6-3 7-6 victory over Li Na to book a place in the semi-finals.
Williams shook off six double-faults and rallied back from 5-2 down in the second set.
"I realized I was down. It was just one point at a time after that," said the world number one Williams.
"The tiebreak was good, it just came down to one point at the end."
(Reporting by Amlan Chakraborty in New Delhi and Jahmal Corner in Los Angeles; Editing by John O'Brien/Ian Ransom)