Rafael Nadal and Novak Djokovic will put their impressive winning streaks on the line at the 5.8-million-euro ATP-WTA Madrid Masters, a key indicator of form ahead of the French Open.
World number one Nadal has been untouchable this clay season, winning a record seventh title at Monte Carlo and backing it up with his Barcelona success last week by lifting a sixth trophy in seven editions at his home event.
He has not lost on clay since the 2009 French Open fourth round against Robin Soderling, a run of 34 winning matches.
Second seed Djokovic came onto the dirt this week undefeated and headlining at his hometown Serbian Open in Belgrade where he was playing Spain's Feliciano Lopez in Sunday's final aiming to take his 2011 record to 28-0.
Though the in-form Djokovic won their last two meetings in the Masters finals at Indian Wells and Miami, Nadal leads the Serb 9-0 on clay.
But looking too far ahead is not the Spaniard's style.
"I'm not worried about Djokovic now," he said.
"I can only play him in the final. My next worry is my first Madrid opponent plus playing well and staying injury-free."
Third seed Roger Federer will be trying to lift his level after just one title in Doha at the start of the season.
The Swiss is bidding for a trophy hat-trick in Madrid after titles in 2006 (on indoor hardcourt) and 2009 with a fighting victory over Nadal. The Spaniard claimed the trophy back from his Swiss rival in 2010.
Federer's last outing was a quarter-final loss to Austrian Jurgen Melzer in the Monte Carlo quarters, with the Swiss getting back on the practise court at home to try and polish his game for the remainder of the claycourt run to Roland Garros, which starts on May 22.
The top eight seeds on the men's side in Madrid have byes into the second round.
Scot Andy Murray will be on court for the first time since injuring his right elbow but still playing a tough semi-final in Monte Carlo against Nadal. The number five then withdrew from Barcelona as a health precaution.
Fifth-seeded Soderling needs to get a workout on the clay after winning three titles from his first four events in 2011 in January and February.
The Swede went out in an Estoril quarter-finals to resurgent Argentine Juan Martin del Potro, who is coming quickly back to form after missing much of 2010 due to wrist surgery.
In the women's draw, Caroline Wozniacki will try to bounce back from last week's Stuttgart final loss as the top seed steps up her preparation for Paris.