As expected, Nils Grandelius was quickly caught; as wasn't expected, he remains in a tie for first. Granted, it's still very early - there are nine rounds left in Wijk aan Zee - but Grandelius is (generally) playing well, and several other underdogs are hanging in there.
In round 3, Grandelius lost on the white side of an Advance French against Pentala Harikrishna. It's a model game for Black, and the result was that the winner caught up with the loser. Had Magnus Carlsen beaten his countryman Aryan Tari, he'd have taken the lead, but he was unable to win. That's a three-way tie. Likewise, had Fabiano Caruana managed to finish a brilliant game against Jan-Krzysztof Duda he'd have taken the clear lead, but he too only managed a draw. That's a four-way tie for first. Anish Giri made it a five-way tie for first when he drew with Alexander Donchenko. The other two games saw Alireza Firouzja defeat David Anton to close to get back to 50%, while Radoslaw Wojtaszek and Jorden Van Foreest drew their game.
In round 4, all seven games were drawn, so the five-way tie for first remained in place. Some players had winning chances, though. Grandelius in particular was winning with Black against Andrey Esipenko, but let the advantage slip away in time trouble. The craziest game of all was Tari vs. Firouzja, which went back and forth in a wild draw that ended after just 30 moves. The razor sharp opening and the game ending when it did might lead one to suspect that this was some sort of crazy prep, but this was not the case. Both players made serious errors that even took their position from winning to losing. It's a great game to analyze, and I'll leave that pleasure to you.
Wednesday is a rest day, and on Thursday we get these pairings.
This will be an important day for the non-world champions in the field, as Magnus Carlsen will have the white pieces against tailender Alexander Donchenko. Carlsen doesn't always manage to catch the leader when he's trailing (though he often does), but when he's leading he's almost never caught.