The top seed at a Masters 1000 event for the first time in his career, Djokovic sank his teeth into the clay season (and Florent Serra) in impressive fashion on Wednesday.  After this relaxing afternoon in the Mediterranean sun, though, his road becomes significantly more arduous against the surging Wawrinka, a perpetual threat on clay.  Although names such as Murray and Youzhny have shuffled off the stage, some engaging tennis lies before us on Thursday, which we will preview in a slightly different manner from usual.  Instead of simply writing a "pick," we'll close the capsules with an upset potential rating between 1 and 10, with 1 as the least likely (virtually impossible) and 10 as the most likely (virtually certain).  Consequently, you'll know not just our prediction but our degree of confidence in it!  Spoiler alert:  there's only one ranking distinctly over 5, but a few others hover very near that number.Djokovic (1) vs. Wawrinka (13).  Visibly brimming with confidence in his opener, the Serb will need it to overcome the Swiss #2, who comfortably dispatched Hanescu for the second time in three days and demolished Gulbis in the second round.  These two played a gripping three-setter in the 2009 edition of Monte Carlo, during which Wawrinka's consistency pushed Djokovic's offensive talents to the limit in an intensely physical match.  As the match reached its climax, Novak rose to the occasion in the crucial moments and probably will do so again. Upset potential:  3.5.Robredo (12) vs. Nalbandian.  Renowned for his sturdy ball-retreiving skills, Robredo makes clay courts feel tiny to his opponents, whom he coaxes into reckless errors.  Despite recently undergoing hip surgery, Nalbandian has rebounded almost immediately to threaten Nadal in Miami before upsetting Youzhny in an epic thriller here.  While the Spaniard seeks to shrink the court, the Argentine will strive to expand it with artfully angled groundstrokes.  He'll likely be weary after a three-hour duel in the sun on Wednesday, and Robredo will test his stamina, but never count him out.  Upset potential:  4.Cilic (4) vs. Montanes.  Generally a little uneasy on clay, Cilic nevertheless delivered an impressively (and rather unexpectedly) gritty performance against Andreev, rallying after losing a marathon first set.  Facing the unimposing Montanes, he'll be the aggressor in most of the rallies.  If he controls his aggression and constructs intelligent points, he'll win routinely.  If he sprays more balls than he ought, he'll endure some tense moments but probably still prevail anyway.  Upset potential:  2.5.Berdych (10) vs. Verdasco (6).  After a breakthrough performance in Miami, Berdych has plowed through his first two matches while surrendering just six total games.  On the other hand, Verdasco was equally "en fuego" during his second-round clash with the overmatched Benneteau.  These power merchants square off for the second straight tournament; Berdych eked out a fiercely contested quarterfinal back on the North American courts.  Although he's enjoyed repeated success against Verdasco, the Spaniard moves more fluidly than the Czech on clay.  He'll likely earn revenge in a hard-fought, high-quality contest.  Upset potential:  4.5.Ljubicic (8) vs. Ferrer (11).  The long-dormant Spanish roadrunner resurfaced during Davis Cup and delivered a solid result in Miami before scoring a pair of uneventful wins here.  The toast of Indian Wells, Ljubicic will find his serve blunted by the surface and his limited movement exposed against the uber-consistent Ferrer.  Upset potential:  7.Petzschner vs. Kohlschreiber.  This all-German match results from Murray's appallingly lackluster performance in his opener, which he ceded to Kohlschreiber in a (mercifully) fleeting 63 minutes.  Not overshadowed by any clear contender, this quarter offers a mouthwatering chance for one of its four inhabitants to reach the semis without knocking off a marquee name.  Kohlschreiber is much more comfortable than his compatriot on clay.  Oh, and he's the higher-ranked player, in case you were wondering.  ;)  Upset potential:  3.Tsonga (5) vs. Ferrero (9).  Another rematch from Miami, where a thunderous Tsonga predictably steamrolled the stylish but far less powerful Ferrero.  Suggesting that this encounter should be closer is the Spaniard's comfort level on clay; the former French Open champion reeled off a 15-match winning streak in South America several weeks ago.  During a dramatic yet erratic victory over Almagro, the clay surface exposed the inconsistencies in Tsonga's high-risk style.  Although Almagro couldn't capitalize on multiple opportunities, the steadier, more patient Ferrero might well do so.  Upset potential:  5.5.Berrer vs. Nadal (2).  On one side of the net stands an aging serve-and-volleyer who has never won a title.  On the other side of the net stands the five-time defending champion and a four-time French Open champion.  Upset potential:  1.***Feel free to let us know what you think of this new format, which we tested just to introduce some variety but which we might revive in the future. Initially, we had planned to release our "plotlines to ponder" for the clay season during this week.  However, we decided to save it for the less action-packed week ahead and channel a little extra attention towards Monte Carlo; don't worry that we've wandered away from the agenda!  ;)