Serbian rivals and frenemies Ana Ivanovic and Jelena Jankovic burst onto the international stage near the same time in 2006-07.  Both women would spend time at the No. 1 ranking in 2008, when Ivanovic won her only major title to date and Roland Garros and Jankovic finished the season in the top spot.  They have scattered 11 collisions, many of them fierce, over nine years and four surfaces.  The most memorable of those came in a 2008 semifinal at Roland Garros.  With the No. 1 ranking up for grabs between the two Serbs, Ivanovic rallied from losing the first set to edge her compatriot.

But their rivalry has faded into a WTA subplot over the last few years.  The Serbs have collided only once since 2011 and only three times since 2008, none of those meetings coming in a quarterfinal or later.  Despite the lower stakes, the emotional intensity always has surged high on both sides when Ivanovic and Jankovic meet.  The Stuttgart spectators thus can expect a charged atmosphere in a Saturday semifinal that marks their first meeting on clay since 2010 and just their third overall.

Ivanovic has advanced with somewhat more difficulty than Jankovic so far, needing three sets to edge each of her last two opponents.  She regrouped from a poor first set to fend off home hope Julia Goerges before edging Svetlana Kuznetsova in a rollercoaster featuring two Roland Garros champions.  Jankovic also needed to rally from dropping a first set this week.  Her comeback came against Indian Wells champion Flavia Pennetta and preceded a more straightforward victory over a former nemesis in Alisa Kleybanova.

While the Serbs have split their two meetings on red clay, Ivanovic has dominated their rivalry overall.  Victories for the younger woman in their two most recent encounters ran her overall record against Jankovic to 8-3.  In many ways, their games are mirror images of each other.  Ivanovic specializes in crafting serve-forehand combinations and bold first strikes, whereas Jankovic built her career on seamless movement, tireless counterpunching, and a smooth two-handed backhand.  The indoor clay of Stuttgart usually favors the more offensively ofriented player, which might give Ivanovic an edge.

It certainly favored the more offensive player in the marquee quarterfinal earlier on Friday, when Maria Sharapova knocked off top seed Agnieszka Radwanska.  The two-time defending champion weathered a match that unwound through 11 service breaks in its 19 games.  Sharapova's relentless pressure on Radwanska's serve led to her second top-10 victory in two tournaments and sixth in three Stuttgart appearances.  Her perfect record at the Porsche Grand Prix remains intact heading into a battle with the WTA's clay specialist par excellence.

Advancing via a third-set retirement from Carla Suarez Navarro, Sara Errani faced Sharapova in the most memorable match of her career.  She played the role of best supporting actress in the 2012 Roland Garros final, when Sharapova cemented her place in the record books by completing a career Grand Slam.  Since that afternoon in Paris, Errani has faced Sharapova three more times without winning a set.  On the other hand, three of their last four sets have reached 5-5 in a trend that suggests a narrowing gap between them.  

None of the Stuttgart semifinalists has won a Premier title this season.  (In fact, only Ivanovic has won a title at any level this season, claiming two International crowns in Auckland and Monterrey.)  One of these four women will start the clay season on a high note, however, while collecting the keys to a blue Porsche perched above the court.  Follow the Porsche Grand Prix semifinals on Tennis Channel, starting at 7:30 AM Eastern time on Saturday.