While the fighting was happening in Greece, Rommel's army was pushing to the east. This action kept any further units from being shipped to Greece. The 2nd Armoured Division lacked effective leadership. The division commander was captured at Mechili. The Indian motor brigade mostly broke out of Mechili and headed towards Tobruk. The armored brigade from the 2nd Armoured Division managed to reach Tobruk. The 9th Australian Division also reached the former Italian fortress at Tobruk.
The Australians were able to secure the perimeter at Tobruk and proceeded to onduct a tenacious defense.
In the chaotic conditions following the German capture of Mechili, you had British Generals driving in the dark, unsure of where they were. Generals Philip Neame and Richard O'Connor made a wrong turn and drove into a German ambush, where they were captured. Previously, at Mechili, General Noel Beresford-Peirse had surrendered to the Germans during collapse of the defense.
East of Tobruk, both Salum (or Sollum) and Halfaya Pass were occupied by Rommels forces. The Germans set up an eastward facing defensive position that included 88mm guns used in an anti-tank role, with 50mm PAK38 and 37mm anti-tank guns
This is based on the account in "Greece, Crete, and Syria" by Gavin Long.