US Open Fast Forward breaks down every match on a busy Monday with Round of 16 action in both singles draws.

Alison Riske vs. Daniela Hantuchova:  Thundering past a feverish Petra Kvitova, young American Riske reached the second week of a major for the first time.  She will face a familiar opponent there, from whom she won a set in Birmingham three months ago before fading to defeat.  Hantuchova reached this stage by the narrowest of margins, needing a final-set tiebreak to defeat a qualifier who had served for the match.  Despite her greater experience, Hantuchova has reached just one major quarterfinal since 2003.  She will expose Riske’s movement by opening the court with her angled groundstrokes, while the American aims to set the tone with her stronger serve.  The home hope might rise to the occasion of a match on Arthur Ashe—or shrink from the spotlight.

Ana Ivanovic vs. Victoria Azarenka:  The encounter of major champions and former No. 1s could be a gruesome blowout, a stirring upset, or anything in between.  Ivanovic owns two victories over Azarenka, one on a fast North American hard court in Cincinnati, but the two-time Australian Open champion has bageled her in each of their last two matches.  The first of those bagels came in a rout at Wimbledon last year, while the second merely began a rollercoaster three-setter in California this summer.  Expect Azarenka to target Ivanovic’s backhand, the area in which she holds the clearest edge.  Only a strong first-serve percentage and pinpoint returning can carry the Serb to the upset past an opponent with steadier, more balanced weapons.

Roger Federer vs. Tommy Robredo:  The second-ranked Tommy in the ATP (after Haas) revived his career during the clay season with two titles and a Roland Garros quarterfinal.  None of Robredo’s key wins this year have come against members of the ATP Big Four, though, and he next faces a man who has bullied him around the world for over a decade.  Federer never has lost to Robredo, David Ferrer, or Fernando Verdasco, seemingly avenging his frustrations against Rafael Nadal on his compatriots.  Three of his ten wins in this non-rivalry have come at hard-court majors, although Robredo did win a set on the last occasion.  Having breezed through the first week, Federer should have nothing to fear on a fast court from an opponent who lacks explosive firepower.

Philipp Kohlschreiber vs. Rafael Nadal:  Still undefeated on hard courts this year, Nadal has looked every inch the title favorite.  The world No. 2 has established early leads in every set that he has played, avoiding any real pressure.  Like Federer, he has dominated his fourth-round opponent on all surfaces because of a matchup especially favorable to his game.  Kohlschreiber’s 1-10 record against Nadal testifies to his lack of an imposing serve or a powerful two-handed backhand, the two shots that most trouble Rafa.  A four-set upset over John Isner did display the German’s shot-making talent, and he has taken sets from the Spaniard in all five of their hard-court meetings.  But three sets is too much to ask for someone as streaky as Kohlschreiber, who plays with little margin for error.

Simona Halep vs. Flavia Pennetta:  Your view of this match will depend on whether you favor experience or the hot hand.  Halep contests a second-week match at a major for the first time in her career, while Pennetta reached this stage at Wimbledon this summer and many times before.  But Halep has lost only two matches since early May to opponents other than Serena.  One of those came via retirement against Pennetta after they split the first two sets.  Both women cut their teeth on clay but have evolved into arguably more dangerous players on faster surfaces.  Upsets over Sara Errani and Svetlana Kuznetsova leave Pennetta positioned to threaten a woman who has not lost more than two games in her last five sets.

Richard Gasquet vs. Milos Raonic:  Most of the summer sensations on the men’s Tour have sputtered to first-week exits, from Vasek Pospisil and Ernests Gulbis to John Isner.  Not so Raonic, who has built on his Rogers Cup final with three relatively straightforward wins here.  He won his only meeting with Gasquet on a similarly fast court in Cincinnati last year, relying on his more imposing serve to end points quickly.  The Frenchman’s elongated groundstrokes reap more rewards on a slower surface, and Gasquet never has left an impact on the US Open.  Still, he snuffed out another surging threat in Dmitry Tursunov a round ago, improving on his tepid play from the Masters 1000 tournaments.  Rarely high in belief, Gasquet will need to show more spine than usual in moments of tension and adversity.

Camila Giorgi vs. Roberta Vinci:  A battle between two Italians offers an inviting opportunity for either of them to exploit an imploded section of the draw.  Vinci seeks her second straight US Open quarterfinal, while Giorgi seeks the first major quarterfinal of her career.  Beware of discounting the younger, more volatile Italian, who mounted a three-set comeback against No. 6 seed Caroline Wozniacki under the lights of an Arthur Ashe night session.  Accumulated fatigue may catch up with Giorgi after playing six matches between the qualifying and main draws.  Someone who can pound 46 winners past a retriever like Wozniacki can outhit Vinci from the baseline too, though, so the elder Italian will look to slow the pace and disrupt the rhythm with weapons like her backhand slice.

Janko Tipsarevic vs. David Ferrer:  When the draw first appeared, many who examined it (including me) felt that Ferrer’s section would implode within days.  That did not happen.  Instead, two men who contested a US Open quarterfinal last year used their soft section to find their form, absent for most of the summer in Ferrer’s case and most of the year in Tipsarevic’s case.  The Serb took the Spaniard to a final-set tiebreak in that 2012 quarterfinal, filled with endless, bruising rallies between two relatively small men.  Ferrer’s ankle injury appears to have receded, and the best-of-five format should help him outlast the more volatile but streakier shot-maker across the net.  The two crisp two-handed backhands on display rank among the finest in the ATP when at their best.