Murray is trying to reach his first quarter-final on clay
Andy Murray recovered from a poor start to lead Italy's Fabio Fognini by a set when rain halted third-round play at the Monte Carlo Masters 1000.
The Briton was leading 7-6 (13-11) 1-0 after recovering from 5-0 down in the opening set on Court des Princes.
Murray will resume at 0930 BST on Wednesday, with a potential quarter-final to follow later in the day.
Roger Federer's struggles continued as he went down 6-4 7-5 to fellow Swiss Stanislas Wawrinka on Thursday.
The world number two, who was supposed to be on his honeymoon with new wife Mirka, had accepted a wildcard into the event as he looks for a first title since October.
"I was making a few too many errors," said Federer. "That kind of gave him the advantage. I thought Stan played well.
I am a bit embarrassed to celebrate
"I'm happy for him that he's progressed so much over the last couple years. He's finally making a push, getting close to top players and beating top players like myself. I think it's great for him."
Federer beat Italian Andreas Seppi easily enough in his opening match but 13th seed Wawrinka, who won the Olympic doubles title with Federer in Beijing, proved far tougher.
The start of play was delayed by over five hours and saw Murray's match moved to the second show court, while Federer took centre stage on Court Central.
But it was Wawrinka who broke serve in the seventh game when he converted his sixth break point, while Federer had yet to manage one.
The unforced errors that have haunted Federer all year continued to flow and, after the pair swapped breaks at the start of the second set, a wild forehand put Wawrinka ahead again at 6-5.
Federer earned two break points as Wawrinka served for the match but the less-heralded Swiss held his nerve and fought back to take his first match point, and claim a first win over his compatriot in three meetings.
"It was not an easy match but of course I am happy to have won it," said Wawrinka. "I am a bit embarrassed to celebrate it."
Wawrinka will face Andreas Beck
for a place in the last four after the German qualifier beat Argentine Juan Monaco 3-6 6-2 7-5.
was in serious trouble as Fognini made a superb start, building on the form that saw him come through qualifying to reach the third round.
The world number 108 stormed into a double-break lead but failed to serve out at the first opportunity and paid the price.
Murray grew in confidence, reeling off five games in a row to draw level before Fognini gathered himself sufficiently to force a tie-break.
And it proved to be an astonishing climax to the set as both players repeatedly took, and threw away, the initiative.
The pair had seen three set points apiece go begging before Murray finally converted the fourth when the Italian missed a smash, and the rain that followed gave Fognini a welcome chance to regroup before the match resumes on Friday.
Third seed Novak Djokovic
beat Albert Montanes 6-1 6-7 (4-7) 6-0 and will next face Spain's Fernando Verdasco
, after the seventh seed thrashed compatriot and 10th seed David Ferrer 6-2 6-1.
World number one Rafael Nadal
came out onto Court Central during a late break in the weather to face Ecuador's Nicolas Lapentti, and the Spaniard was clearly not happy at being asked to begin his match in poor conditions.
Lapentti held serve to lead 1-0 when the rain began to fall again, bringing an end to Thursday's play.
Like Murray, Nadal faces the prospect of playing two matches on Friday as he will resume against Lapentti at 0930 BST, with the winner facing Ivan Ljubicic or Simone Bolleli later in the day.