We found out that being opposite Willard is easier to take him down and get the artifacts. From the starting position, Willard is exactly on the opposite side and he will move to the either left or right. In any case, do not move at all.

Let's say that he moved to the left (anti-clockwise). Start shooting at him (you need about 12 Desert Eagle bullets) until he is stunned. Even if you see him close to you, do not move or you may fall into a lava pit. 95% he will fall between the hallway you are standing in front and the hallway on the left.

Once he is down, run to the right, pass the first hallway (not the second) and stand exactly opposite Willard (between two hallways). Do not try to get any of the artifacts yet, because you do not have time, as he is about to wake up.

Once he wakes up, you should be opposite each other. Start shooting at him again and if it is possible, side step to the right towards the next hallway (the one opposite the starting position).