The European Club Cup has been a mixed bag at best for the top players thus far, four rounds into the seven-round tournament. Let's start at the top, with Magnus Carlsen. After taking the first round off, he won in trademark style against Vladimir Potkin, creating enough little problems to give his strong opponent the chance to hang himself, which he duly did. In rounds 3 and 4 he drew. That wasn't a bad result in round 3, as Black against Radoslaw Wojtaszek, but the round 4 draw with White against Alexander Donchenko (2610) was another story. Carlsen played some very weird-looking chess - maybe deliberately, to have some fun - and after achieving nothing with it for a while suddenly got an opportunity after Donchenko's 26...h5(?). Had Carlsen played 28.Re3 or 29.Ree4 he would have had good winning chances; missing (or rejecting) both chances, the game finished in a perpetual.
The second highest-rated player, Shakhriyar Mamedyarov, has only played two games: a win in round 1 against an IM, and draw with Black in round 4 against Zahar Efimenko. If anyone missed any chances in the latter game, it was Efimenko, who appeared too happy to make a draw with his elite opponent.
The third highest-rated player is on the verge of becoming #2 in the tournament, and #3 in the world rankings. Ding Liren has gone 2.5/3, grinding out a win with Black against an IM in round 2, drawing with Jan Werle in round 2 (Ding went a bit too all-out for the attack - it was better to maintain the center rather than throwing all the eggs into the kingside basket with 14.e5 - but fortunately for him Werle was happy to make a draw and didn't press for more), and then he was just the latest guy to capitalize on Peter Svidler's blunderful form.
Svidler is having a nightmarish event, losing all three games he has played (and 17.8 rating points) on major errors (as opposed to being outplayed a bit at a time). He was winning a complicated fight against Aleksandar Indjic in round 2 until he played 38.Qxa6, allowing Black to save the game, and then got a second chance to regain a decisive advantage on move 40 with c4. Instead, he had to find the right move to save the game on move 42, but didn't manage. Only 42. g3! would save the game, ensuring that the Black king could not escape from checks by navigating his way through White's kingside pawns. The key variation is 42.g3 Nb2 43.Nb6! Nd3! (everything else loses for Black) 44.Qd6! R7xb6 (the only winning move in the 42.g4 version of the line) 45.Qe7+ and White has a perpetual. With the pawn on g4 instead of g3, Black's king can escape to f4 or h4.
In round 3 the position was complicated but level against Romain Edouard until Svidler played 32.Qf3?? instead of 32.Kg1, hanging the h-pawn. Perhaps Svidler thought he'd be okay after 32...Qxh2+ 33.Kf1, but the nice 33...f4! spoiled the illusion. Granted, 32.Kg1 Re2 33.h4 seems scary, but Black has no way to break through to White's king.
Finally, Svidler was suffering almost the entire game against Ding Liren after surrendering the center early on, but thanks to a combination of resilient defense on his part and looseness on Ding's side of the board Svidler had a chance to make a fight of the ending with 38...Kf7. Instead, he played 38...Nxa2??, and after 39.Bd2 found his knight dominated. This couldn't have come as a surprise to Svidler, as it's a basic pattern, so he either banked on 39...a5 or 39...b5 (the move chosen), only to realize that neither move worked. The problem with the former is that while the knight gets a momentary reprieve after 40.Bxa5 Nc1, it's "recaught" after 41.Bb4!, e.g. 41...Kf7 42.Rd1 Nxb3 43.Rd3 Nc1 44.Rf3+ Ke6 45.Bd2 and the knight will be collected in at most three moves. He tried 39...b5 instead, but 40.b4 (preventing ...b4 followed by ...Nc3) caged the knight, and Svidler resigned after 40...Kf7 41.Rd3, not needing to see Ra3xa2.
Other members of the 2700 club have given up plenty of draws, but I think only three others have lost to non-2700s: Pentala Harikrishna lost to David Howell (who came into the event 2689 and is now over 2700 on the live list, so that's not much of an upset), David Navara lost to Nils Grandelius (2655), and in what I think was the most notable upset so far, Wang Hao (2722) lost to Nemeth (2484).
All these games can be replayed here (without notes, sorry).