Serena Williams vs. Madison Keys: Australian Open 2015 Semifinal Score, Reaction

For a moment, it appeared Madison Keys would make history by toppling two Williams sisters in as many days. Serena Williams' jaw-dropping serve and a nagging leg injury for Keys ensured her potential glory stayed in that fleeting moment.

Williams, the world No. 1, advanced to her first Australian Open Final in a half-decade Thursday, taking down the unseeded teenager Keys 7-6 (5), 6-2, in a match that was far more competitive than most expected at points.

"

Hey, Nineteen! @serenawilliams outplays 19yo Madison Keys, win away from Slam title #19. Serena-Maria final 3am ET Saturday.

— Chris Fowler (@cbfowler) January 29, 2015"

Keys opened the match by breaking Williams' first serve and rarely lost her edge from there, playing with a competitive zeal that often made her look like the aggressor. But the veteran Williams advanced by holding steady for her second straight match, using her first-serve advantage and limiting critical mistakes.

Williams hit 13 aces and won 71 percent of her serve opportunities, doing a better job of keeping her first serve in play than she has throughout the tournament. The top-seeded American nearly won a better percentage of her second-serve chances than her first—a stark deviation that allowed her to fight against an opponent who looked physically superior at points.

Unlike a majority of the tour, Williams' power didn't overwhelm Keys. Not only did she pack a punch of her own, but the 19-year-old consistently made difficult shots on the run to win points that left Williams shaking her head. It's not hard to see this match going a bit differently had Keys not been dealing with a lingering thigh injury.

Both women entered the match at less than 100 percent. Keys tweaked a thigh problem that's been bothering her off and on since before Wimbledon last year, while Williams has been dealing with a stomach virus.

"I've been sick the past few days, and it's just getting worse and worse, but hopefully it will get better," Williams told reporters. "I heard there's a virus going around with a lot of the players, and I think I caught it."

Whereas Keys' thigh injury was obviously a storyline throughout the match—she could be seen wincing and grabbing at her taped-up muscle—Williams showed no signs of illness. After a competitive first set that saw the two women trade breaks and then battle through a hard-fought tiebreak won by Williams at 7-5, Serena actually appeared to get stronger as the match went along.

"

Serena is 14-1 in Slams after winning 1st set in tie-break. Top seed hasn't lost tie-break on tour since 2013 US Open final. #ESPNTennis

— ESPNTennis (@ESPNTennis) January 29, 2015"

She broke Keys' first serve and went about picking apart the carcass of her obviously weakened opponent. Avoiding mistakes and keeping her serve under control, Williams was able to play an almost uncharacteristically defensive match as Keys fell apart. The youngster committed 39 unforced errors, including 21 in a second set in which she had just 11 winners.

Keys' high-octane style was similar to the way she defeated Venus Williams, but Serena was far better at covering her ground and avoiding the mistakes that befell her sister. Keys' 27 winners were seven fewer than she had in the previous round. Ultimately her big win of the match was battling through seven different match points for Williams to earn a point at 5-2.

It wound up taking Williams two more to finish the job.

Williams advances to the final to face Maria Sharapova, who defeated Ekaterina Makarova in straight sets during their semifinal matchup. Sharapova and Williams obviously have one of the most storied rivalries of this generation. Playing Williams has long been an Achilles' heel of Sharapova's, who has dropped 15 straight and 16 of 18 career matches against Serena.

"For whatever reason, Maria gets under Serena's skin," Lindsay Davenport, who coaches Keys, recently told Bruce Matthews of the Sunday Herald Sun. "Serena is always at her best against her because in her mind, she almost refuses to lose."

Williams has defeated Sharapova twice in Melbourne, including a 2007 finals win. Only once in their last 10 head-to-head matchups has Sharapova even taken a set. Davenport said Williams has such success against Sharapova in part because she hits the ball in a similar style to her sister, Venus.

"It's funny, Maria hits the ball similar to Venus. It's very flat and heavy and I truly think Serena grew up hitting that ball for her whole life," Davenport said. "So the pace doesn't affect her, the heaviness of the shot doesn't affect her."

Sharapova's lone title Down Under was in 2008, and while she's reached the final two other times, she's far from favored against arguably the greatest women's hard-court player ever. That said, Sharapova's been nearly flawless over the last couple of weeks. She hasn't dropped a set since her second-round scare against Alexandra Panova, not allowing an opponent to win more than three games in a single frame.

Alan Diaz/Associated Press

This is by far the best Sharapova has played on a hard surface since she dropped the 2012 Australian Open final to Victoria Azarenka. If there is any time to beat the streak, Saturday will be it. History, though, says we should probably bank on Williams starting 2015 as she finished 2014: a major champion.

Follow Tyler Conway (@tylerconway22) on Twitter