The top-seeded American completed her quest for the "Serena Slam" with a 7-6 (7-4), 3-6, 6-4 victory over Venus in the Australian Open - her fourth win in a row over her sister in a major final.
"I never get choked up but I'm really emotional right now," Serena said after receiving the Daphne Akhurst Memorial Cup.
Serena became just the fifth woman to hold all four majors simultaneously, joining legends Maureen Connolly, Margaret Court, Steffi Graf and Martina Navratilova, and the ninth to have won each of the four Grand Slam singles titles.
Connolly, Court and Graf won traditional Grand Slams
- capturing all four majors in a calendar year - and Navratilova and Graf recorded four straight Grand Slam triumphs in non-calendar year situations.
Not only did Serena take the upper hand in their head-to-head confrontations, 6-5, but she now owns a 5-4 lead over her older sibling in Grand Slam titles.
Venus went into the match having not dropped a set during the tournament, but came up short in a bid for her 29th career title.
"I wish I could have been the winner today but you've a great champion with Serena," Venus said. "Now she's won all four Grand Slams which is something I'd like to do one day."
The sisters made history by becoming the same duo to contest four straight finals at a major. Having had to miss last year's Australian Open with an ankle injury, Serena has not lost a Grand Slam match since falling to Venus in the final of the 2001 U.S. Open.
Serena and Venus were making their first appearance in the Australian Open final. It also was the first time an entire women's singles championship match had been played under a closed roof.
With the temperature reaching 106 degrees - 113 on the court - the organizers invoked the Australian Open's Extreme Heat policy, which closes the retractable roof at Rod Laver Arena.
The first final at Melbourne Park, between Steffi Graf and Chris Evert in 1988, was started with the roof open but completed indoors because of rain.
The matchups between the sisters, who, at 15 months apart in age, are best friends and parctice partners, have featured lots of mixed emotions and many errors.
Saturday's two-hour, 22-minute meeting was no different, with Serena totalling 54 unforced errors - including five double faults - with 37 winners, and Venus recording 51 unforced errors - six double faults - and 28 winners.
Serena fought off two break points in the third game of the match and jumped out to a 3-1 lead. But Venus broke back in the fifth game and later broke for a 5-4 advantage.
Serena clearly was disgusted with her own play, throwing her racket toward her chair on the changeover. She came out blazing in the next game, breaking her 22-year-old sister when Venus' backhand hit the net and fell back on her side of the court.
Serena held serve and had a set point on Venus' serve, but Venus nailed a inside-outside forehand winner and fired an ace on game point to send the set to a tiebreaker.
Serena blew off more steam in the tiebreaker. When there was a close call on a point she ultimately won, she asked the baseline line judge, "You just won't call them out will you?"
Serena raced out to a 5-1 lead and won her ninth straight set against her sister when Venus hit a forehand long. The winner of the first set has won each of the 11 meetings between the two.
Venus became more aggressive in the second set and broke for a 4-2 lead. She fell behind 15-30 in the next game, but hit a pair of aces and won a point at the net to go up, 5-2. Venus fired her seventh ace of the match to close out the ninth game and send the match to a third set for only the third time in the rivalry, and first at a Grand Slam.
Serena returned to taking advantage of her opponents' weaker second serve and took a 2-0 lead in the third set. But she double faulted on double-break point in the next game and Venus held serve to even things, 2-2.
Venus staved off three break points in the eighth game to keep the match even. But after Serena held serve for a 5-4 edge, Venus hit a backhand long and dumped in a double fault to set up two match points for her sister. A cross-court forehand hit long by Venus gave Serena her 20th career title.
Friday, the sisters captured their second Australian Open women's doubles crown. The top-seeded duo defeated the second-seeded pair of Virginia Ruano Pascual of Spain and Paola Suarez of Argentina, 4-6, 6-4, 6-2. It was their sixth Grand Slam doubles title.