Image source, AP

Wonder what is going through the mind of these two people in the Federer box. Panic probably. Roger's wife Mirka and coach Stefan Edberg cannot do much from the Roland Garros stands - other than hope for some vintage Roger magic - as Wawrinka holds serve to move within one game of the second set.

Piers Newbery watching Nishikori v Tsonga
BBC Sport at Roland Garros

"After an interruption of half an hour, some spectators return to the seats vacated when a piece of the huge TV screen in the corner of the stadium blew away in the wind and crashed down on them.

"An ambulance arrived in the tunnel below the stadium, with reports of two injured people being taken away for treatment. Finally, play gets underway way again, and Tsonga immediately drops serve when trying to close out a two-set lead."

Image source, Getty Images

Well what have we here?! A Stan Wawrinka-shaped upset, that's what. The Swiss number eight seed sets up a break point with a stinging forehand winner and snaffles that chance at the first attempt as Federer's forehand volley misses the target. Wawrinka takes control of the second set....

Forehand power is the key phrase here. Wawrinka is playing like a pneumatic drill which has been charged up overnight in the garage. Federer can barely stick a racquet on Wawrinka's serve, slipping 40-0 behind, briefly nicking a point back, before the formality of the sixth game is completed.

After a 20-minute break, the other quarter-final resumes on Philippe Chatrier following that earlier mishap (see 16:16). Home favourite Jo-Wilfried Tsonga, the 14th seed, is serving for the second set against fifth seed Kei Nishikori.

"Anything Stan can do, Roger can do (almost) better." It is not quite a Broadway musical, but this match is well worth the admission fee. Federer hammers down a flurry of serves, finishing with a thumping serve, to hold serve to love.

No separating these two Swiss stars in the opening stages of the second set. Wawrinka holds serve pretty comfortably - and quickly - to restore parity.

Simon Cambers
Tennis journalist on BBC Sport online commentary

"Federer has set such high standards over the years that you expect him to make every shot but Wawrinka is outplaying him.

"When you have a head-to-head record that is so against you then you must start well."

Image source, AP

Not sure how long Wawrinka will be able to keep up this intensity. The 30-year-old has three years on his illustrious compatriot and is using his relative youthfulness - and power - to pin back Federer. He pegs the server back to 40-30, before Federer resumes control to hold.

Routine hold for Wawrinka. Federer again has few answers to his opponent's serve and world number nine Wawrinka wraps up the game quick sharp. Not much more to say really...

While Nishikori and Tsonga wait for the green light, the action is back under way on Suzanne Lenglen. And thankfully the quality of these two Swiss rivals is showing no signs of slowing down. Wawrinka charges out of the blocks again, forcing Federer into defending another break point. Again, the world number two manages to wriggle out of a tight spot to save.

Piers Newbery watching Nishikori v Tsonga
BBC Sport at Roland Garros

"The umpire announces that another 10 minutes will be required to secure the area properly and the players head for the locker room, while officials begin the task of seating the displaced spectators.

"The main concern is that everybody is OK; a secondary issue is this is one of the few matches of the fortnight where Chatrier seems pretty much full.

Image source, Reuters

Play has been suspended momentarily on court Philippe Chatrier as safety officials clear up the debris. Television pictures show us that the gusty wind at Roland Garros whipped off a piece of the television screen which fell on the crowd below. Thankfully the person who seemed to take the full force is giving it the thumbs up.

Simon Cambers
Tennis journalist on BBC Sport online commentary

"Wawrkina deserved the set, he's been the aggressor, he's hitting the big shots and has taken the game to Federer. He's playing very well and looks like he believes he can do it.

"Wawrinka was always talented but mentally didn't seem to think he belonged with the likes of Federer but he does now. He's a fantastic player."

Image source, AFP

Wawrinka serves for the set. Can he complete 46 minutes of good work?

We've already seen Federer go tumbling - now it is time for Wawrinka to eat clay. Stan slips as he watches a Federer backhand slip agonisingly out of his grasp. That means Fed leads 30-15 before Wawrinka starts working that Federer backhand good and proper.

After a longish rally Federer finally buckles for 30-30, but Wawrinka is left shouting in frustration as he gifts his compatriot a break point. But Federer can't take it.

Wawrinka digs deep, serves big and produces an impressive save in deuce to take the first set.

Piers Newbery
BBC Sport at Roland Garros

Image source, AP

"A very worrying moment on Chatrier as a piece of hoarding comes way high in the stands, presumably blown by the wind, and apparently hits spectators.

"One man is led away by paramedics with his arm in bandages, albeit smiling and waving with the other hand.

"Play is halted as they try to tape off the area and move spectators elsewhere. Tsonga and Nishikori sit on their chairs and wait."

Simon Cambers
Tennis journalist on BBC Sport online commentary

"The extra physicality, that extra bit of weight perhaps, is working in Wawrinka's favour. It seems to give him a bit more power."

Back to the wall time for Federer. Wawrinka earns himself a set point as his sheer power forces Federer into another error. But when the going gets tough, Federer gets going. A forehand volley and another passing winner sees off the danger. For now at least....

Federer serves to stay in the first set. After an unforced error on the first point, he spanks down an ace to go 15-15. But the pounding returns soon, er, return. Wawrinka edges 30-15 ahead and then forces deuce as Federer roars back...

Image source, Reuters

Let's see if Federer heeds Simon Cambers' advice. Not on the first point. Federer stays back and can't touch a Wawrinka forehand. Wawrinka lets one go with a poor backhand, but steps up a gear to beat Federer - and the increasing Paris wind - with some brute force.