Martell Taylor-Crossdale opened the scoring for Chelsea after 14 minutes at Aldershot, but Vladamir Dragomir (pictured above, with Harvey St Clair) equalised just four minutes later.
Chelsea, featuring Charly Musonda in their line-up, restored their lead when Dujon Sterling pounced after Kylian Hazard’s effort had been saved by Dejan Iliev.
But with Chelsea seemingly on course for their first win in eight matches Willock struck at the death.
The point leaves the Gunners fourth in the table, ahead of Sunday’s matches, while Chelsea lie 10th.
CHE: 18 Nov v Spurs (A)
ARS: 17 Nov v Porto (H) – PL International Cup