Tomas Berdych, Mardy Fish and Juan Martin del Potro have all advanced to the second round of the Australian Open on Monday at Melbourne Park but their fellow seeds Fernando Verdasco and Jurgen Melzer crashed out.
Czech No.7 seed Berdych, who was a quarter-finalist at last year's Australian Open, didn't have it all his own way as he was forced to work for a 7-5 4-6 6-2 6-3 win over Spaniard Albert Ramos.
Eighth-seeded American Fish, who reached the last eight at Melbourne Park five years ago, spent just over two hours on Show Court 3 before emerging with a comfortable 6-4 6-4 6-2 victory over Gilles Muller of Luxembourg.
Spanish 10th seed Nicolas Almagro fell behind early in his Court 6 battle with Poland's Lukasz Kubot but battled back to win 1-6 7-5 6-3 7-5, as did 2009 US Open champion del Potro, the Argentine 11th seed coming from a set down to see off stubborn Frenchman Adrian Mannarino 2-6 6-1 7-5 6-4.
But rising local star Bernard Tomic recovered from a two-set deficit to send Spanish 22nd seed and 2009 semi-finalist Verdasco packing 4-6 6-7 (3-7) 6-4 6-2 7-5, a couple of hours after Croatian Ivo Karlovic had dumped Austrian No.31 seed Jurgen Melzer 7-6 (7-3) 7-5 6-3.
Spanish No.18 seed Feliciano Lopez tamed Argentine Leonardo Mayer 7-6 (7-5) 6-3 7-6 (7-2), Swiss No.21 seed Stanislas Wawrinka cruised to a 6-1 6-1 7-5 win over Frenchman Benoit Paire and South African 30th seed Kevin Anderson had a straightforward 6-1 6-2 6-4 win over Dane Frederik Nielsen.
While Berdych will next meet Belgian Olivier Rochus after he beat German Bjorn Phau 6-1 6-4 6-0, Fish will take on Colombian Alejandro Falla following his 6-3 6-2 3-6 6-1 victory over Italian Fabio Fognini.
Almagro now awaits the winner of the match between Frenchman Jeremy Chardy and Bulgarian Grigor Dimitrov while del Potro's win set up a second-round clash with Slovenian Blaz Kavcic, who dumped British qualifier James Ward 6-4 6-3 6-4.
Tomic earned himself a shot at American Sam Querrey, who beat Frenchman Kenny de Schepper 6-3 6-2 6-2, while Riba is now preparing to take on either Argentine 25th seed Juan Monaco or German Philipp Kohlschreiber.
German Tobias Kamke thumped Romania veteran Victor Hanescu 6-2 6-1 6-2 to earn a shot at either Ukrainian 13th seed Alexandr Dolgopolov or Australian wildcard Greg Jones, while Karlovic will next battle Argentine Carlos Berlocq after his 2-6 6-3 7-6 (7-3) 6-3 defeat of Dutchman Jesse Huta Galung.
Anderson's reward for his win is a clash with Sergiy Stakhovsky, who came from 2-5 down in the deciding set to win an all-Ukrainian duel with Illya Marchenko 6-3 6-7 (9-11) 4-6 6-3 7-5.
Wawrinka will be scouting the match between 2006 finalist Marcos Baghdatis and German Benjamin Becker, while Lopez will now play Italian Flavio Cipolla after he outlasted Russian veteran Nikolay Davydenko 6-4 4-6 3-6 6-2 6-1.
And Haas may be through to the second round for the 10th time from 11 attempts at an event where he has three times been a semi-finalist but he's likely to run into world No.2 Rafael Nadal, provided the 2009 champion gets past American Alex Kuznetsov.