Jonathan Davies: Ospreys and Blues can ride the tide of Wales' Grand Slam glory

We'll find out today if the tidal wave that took Wales to the Grand Slam has enough impetus left to carry the Ospreys and the Cardiff Blues into the Heineken Cup semi-finals.

Success is contagious and all players based in Wales have either experienced or seen at close hand what you can achieve if you believe in yourselves. Their confidence will undoubtedly be boosted and it will need to be, because the harsh realities awaiting at this stage of the cup will soon sort out any doubters.

It worries me a little that the Ospreys are such clear favourites to win on their visit to Saracens. They have every right to be fancied after their clear victory over Sarries in the EDF Energy Cup a fortnight ago, but home advantage in the Heineken Cup is always a powerful factor.

The Ospreys dominated the last meeting by playing fast and direct, controlling play up front before bringing in the backs to apply the finishing touches. They have to play at a high tempo again today, but with Justin Marshall at scrum-half it will be a slightly different approach.

Had Mike Phillips not suffered the injury that is going to keep him out for six months, I am not sure who would have started at No 9. It would have been a very interesting choice. Phillips is the more direct and forceful player, always dangerous around the fringes, while Marshall is more of a tactician, excellent at bringing others into play. There is not another team in the world who possess such a brilliant rivalry for the scrum-half spot. To have Marshall is a massive plus, as is having his fellow All Blacks, the back-rowers Marty Holah and Filo Tiatia, in the squad.

A high tempo is going to be important because if the pace is slow, Saracens can sneak into the game. They are a tough Guinness Premiership outfit and they can lift the physicality when they need to. They won't mind if the game becomes a slow and dogged struggle, because that is what they are used to every week.

The Saracens pack won't care to be blown away again, and knowing Andy Farrell he will remember the hand-off he got from Gavin Henson when the centre raced through to score in Cardiff. It is going to be a hell of a battle but the Welsh heroes in the front five and Ryan Jones, Henson, Lee Byrne and the miraculous Shane Williams will take some resisting.

My BBC colleague Jerry Guscott reckons that the Ospreys could become the biggest and best side in the UK. He sees far more of the Premiership than I do and he certainly won't get an argument from me.

The Blues have similar ambitions, and potential, but their owner, Peter Thomas, feels they need to strengthen one or two departments. Outside-half is one of them. They lost Nicky Robinson at the start of the season and a lack of efficient cover has been the downside to a team with a thrilling mix of top-class experience, in Martyn Williams, Xavier Rush, Tom Shanklin and Ben Blair, and hugely promising youngsters such as Jamie Roberts and Tom James.

They were hoping Robinson would be back today. He had 20 minutes of first-team rugby last week but it has been decided not to risk him; the promising Wales Under-20 Dai Flanagan gets a chance to build on recent impressive performances.

There is not a more difficult match on the European calendar than Toulouse away. Playing in front of 35,000 is an experience every team has dreaded since this cup came into being.

Almost everyone has written off the Blues' chances but they have a very strong pack who are on top of their form, their backs are going well and their defence is solid. If they can carry the same self-belief Wales had, they most certainly have a chance.

Toulouse love to play open rugby, which would suit the Blues. If Flanagan can open the French up, he is surrounded by players able to take the initiative.