ANDY MURRAY admits Wimbledon's top contenders have been put on high alert after two-time champion Rafael Nadal's shock second-round exit.

Murray was on course to face Nadal in the quarter-finals at SW19, but the Spaniard crashed out in four sets to world No.102 Dustin Brown on Thursday night.

It means the draw has opened up for the British No.1 after eighth seed David Ferrer, also placed in Murray's quarter, withdrew from the tournament through injury.

But Murray insists Nadal's defeat proves nothing can be taken for granted.

"When that happens it's always a bit of a warning to everyone else," Murray said.

"The depth of tennis just now is very high and upsets happen, and for sure they happen more than they did a few years ago."

Murray's consistency against lesser opponents is impressive given the 28-year-old has reached 17 consecutive grand slam quarter-finals.

He will be confident of avoiding an upset against Seppi too, after winning their last six encounters without even dropping a set.

"I expect a tough match," Murray said. "He made the final in Halle two weeks ago and he beat Roger (Federer) in Australia, so he's a very dangerous opponent.

"It's going to be an extremely difficult match to win."

Meanwhile, Murray's coach, Jonas Bjorkman, believes James Ward has the fighting spirit to take his best-ever grand slam adventure even further by beating Vasek Pospisil today.

Londoner Ward blasted past rising Czech star Jiri Vesely to reach the third round of a grand slam for the first time, finally cracking the world's top 100 rankings aged 28.

Ward practised with Murray at Wimbledon's Aorangi Park courts in preparation for the meeting with Pospisil, leaving onlooking Swedish coach Bjorkman impressed.

"It's a great tournament for James already and he's got a great opportunity to go even further still," Bjorkman said.

"He's a great guy. Obviously I haven't seen him playing much before I started working with Andy, but he's a great guy.

"Obviously he had a tough start to the year, with not winning so many matches. It's always hard when it doesn't go the way you want, but now he's been putting it together and been playing some good tennis.

"When things aren't going well, you've got to keep your belief, keep fighting. James has shown that's what he can do and he'll definitely be proud of that.

"When you work hard and you're not winning matches then all of a sudden finally get a few wins under your belt, you normally gain a lot of confidence. So hopefully he can keep that momentum."

Murray's coaching team of Bjorkman and Amelie Mauresmo put both the Scottish two-time grand slam champion and Ward through their paces at SW19 yesterday.