MELBOURNE, Australia (AP) -- Serena Williams has had bad luck with nagging injuries at the Australian Open in recent years.
On Sunday, the top-seeded Williams lost to No. 14-seeded Ana Ivanovic in the fourth round while dealing with a bad back. Last year, Williams lost to Sloane Stephens in the quarterfinals while hampered with ankle and back problems, and two years ago, she was defeated by Ekaterina Makarova while playing on a sore ankle.
Still, Williams wasn't using injury as an excuse after her defeat to Ivanovic, praising the Serbian player's aggressive play and ruing her own costly mistakes.
''I made a tremendous amount of errors,'' she said, ''shots I missed I normally don't miss. I haven't missed since the '80s.''
Williams doesn't lose often these days - she's coming off a 2013 season in which she won 78 of her 82 matches, after all. So her loss at the Australian Open changes the dynamics of a tournament she was the heavy favorite to win.
Here are five things to know about Williams' defeat at Melbourne Park:
END OF A STREAK: Before falling to Ivanovic, Williams had been on a 25-match winning streak. It was the second-longest winning streak of her career, trailing just her 34-match streak that she also posted last year. It was also her first loss to Ivanovic, who had never even managed to take a set off Williams in four previous matches.
MELBOURNE DROUGHT: What was once Williams' most successful slam has suddenly become the toughest for her to win. Five of Williams' 17 Grand Slam singles titles have come at the Australian Open - but none since 2010. In that time, she's picked up two Wimbledon titles, two U.S. Open titles and a French Open title, meaning her current longest Grand Slam drought is here in Melbourne. Williams didn't seem fazed by this fact after Sunday's loss. ''I have done pretty well here,'' she said. ''I feel like I'll win it again.''
OPEN DRAW: Williams' departure opens up her half of the draw significantly. Three other top-10 players have already departed - No. 6 Petra Kvitova, No. 7 Sara Errani and No. 9 Angelique Kerber - leaving No. 4 Li Na as the highest-ranked player in the top half. Both Li and Ivanovic are former French Open champions - the Chinese star won in 2011; Ivanovic won at Roland Garros in 2008. Li has reached the final at the Australian Open in two of the last three years, making her the favorite to advance out of this section.
No. 2-seeded Victoria Azarenka, No. 3-seeded Maria Sharapova and No. 5-seeded Agnieszka Radwanska are on the other side of the draw. They play their fourth-round matches on Monday.
NO CALENDAR-YEAR GRAND SLAM: Given how dominant Williams was in 2013 - finishing with a career-best 11 titles including two majors - many observers had tipped her as a favorite to complete a Grand Slam this year - capturing all four majors in the same calendar year. Nobody has achieved the feat since Steffi Graf in 1988, though Williams did win four consecutive majors - which she dubbed the ''Serena Slam'' - from the 2002 French Open to the 2003 Australian Open.
''I have given up on that a long time ago,'' Williams said of a calendar-year Grand Slam. ''Maybe I can win four in a row, but it seems like in the one year it's kind of difficult for me, for whatever reason.''
RENEWED ANA?: The victory over Williams is a breakthrough of sorts for Ivanovic. Yes, she's won a Grand Slam title, but that was nearly six years ago at the 2008 French Open. Since then, she's been a non-factor at the majors, reaching the quarterfinals just once, at the 2012 U.S. Open.
Against Williams, though, she looked like the Ivanovic of old - the player who briefly reached the No. 1 ranking in 2008. Still only 26, Ivanovic has plenty of time to win another major. ''I'm not afraid going deep against these players,'' she said. ''You know, I feel ready and I want to challenge everyone out there.''