The two people that have surprised me most in London are Robin Soderling and Roger Federer.
To be honest, Soderling didn't shock me too much against Rafael Nadal. I think Nadal's got problems, and in many ways he's probably the weakest link in the eight-man field at the moment, so a straights-sets loss to Soderling was no great surprise for me.
I was surprised he beat Djokovic.
Djokovic is telling anyone who'll listen how tired he is and I can understand that, but Soderling is playing very well and he's going to be a threat.
I still don't see him as the winner of the tournament but he's going to challenge, especially as he's done so well so far. Soderling does get nervous; I thought that might happen against Djokovic, but he didn't have the time.
If it gets tight in the semi-finals, could possibly against Murray, I'd fancy the Scotto win.
I probably underestimated how tired Djokovic is - I had him as favourite coming into the event. I can still see him winning it, but obviously I'm less confident about that now.
Djokovic is always keen to let people know when he is ailing. Whether that's sub-conscious or conscious I'm not sure but we've seen it with his injuries.
Sometimes he's accused of making too much of them, I don't know about that, but we all know how tired he is now. The excuse is out there and I have a feeling he'll have a dramatic revival.
I do not doubt that he is as tired as he says, but I think the adrenalin will see him though on a short-term fix. With all this tournament means, I think he'll find an extra adrenalin rush to see him through to the weekend.
Murray also looked pretty flat at the end of his match against Federer. I was a little alarmed in the last two or three games. Perhaps he was a victim of the round-robin format where you know you can loss and still go through.
I still think he will go through and maybe there's another Federer match waiting in the final of Sunday. But I underestimated Federer. I didn't think he would be capable of the kind of tennis he is starting to produce.
The second set against Murray and the start of the third - when he really put Murray to bed - were superb. I wasn't sure he had it in him this week.
It's been a momentous year for Federer but he wasn't consistently playing the kind of tennis that he had in previous years. But I'm now seeing Federer as a possible winner of the tournament - unlike when it began.
You can't say he's been a revelation because you should never be that surprised by Federer, but I've bheen surprised by how well he's found his form.
He looked pretty flat early on against Fernando Verdasco and I thought his form would remain at that level. But it hasn't, he's raised his game. He raised it when he needed too against Murray and he's been pretty classy in his opening two matches.
I don't think Murray's serve is a long-term problem, it happens. You wouldn't have wanted it to happen on such a feature match but it did.
I was a little surprised Murray fell away so dramatically at the end of the match but if he gets another crack at Federer I don't think that will happen again.
I don't think there will be a repeat of the cataclysmic slide out that we saw on Tuesday night.
Juan Martin Del Potro looked good against Verdasco but I see Federer beating the Argentine. It won't be easy but the way he's playing I see him winning that clash.
I also see Murray beating Verdasco and Murray going through as the second player of that group.
And in the other group, I think Djokovic will still qualify as the runner-up; I think he'll be able to lift himself.
I'm not as confident as I was about Djokovic but I'm reluctant to change who I back to win it.
I had Djokovic and Murray to win this tournament, Federer wasn't one of my favourites. He's certainly joined them, and I would be foolish to not include him now.
There are a few glitches with the tournament. It looks terrific, it looks like a very big event but there are a few problems to sort out.
The main thing is the players have been saying that sometimes they have problems with the lighting.
It looks great on TV though and I think it's a first-class venue.