In The Call of the Wild, how does London create suspense in the scene in which Buck pulls the thousand-pound load?

In chapter 6 of The Call of the Wild, Thornton makes the rather foolish boast that Buck can pull a sled loaded with a thousand pound weight. To make things interesting, a man called Matthewson makes a large bet—$1,000, which was a lot of money in those days—which Thornton reluctantly covers. Other men soon get in on the action, seeing how much money they can make out of Buck pulling the large, heavy sacks of flour piled up on the sled.
It seems like an impossible challenge, but if any dog can do it, Buck can. Nevertheless, even though he's such a strong, hard-working animal, it's by no means certain that Buck will succeed. And for a while, it's touch and go, which makes this passage so full of suspense. One of Buck's feet slips, eliciting an audible groan from one of the spectators; the sled's only moving forward a couple of inches at a time, in a jerking movement. Note how London uses ellipses (. . .) to generate tension and to illustrate just how hard this test of strength really is:

The sled lurched ahead in what appeared a rapid succession of jerks, though it never really came to a dead stop again . . . half an inch . . . an inch . . . two inches . . .

London creates additional suspense by describing the reaction of the crowd of men that's gathered to watch this extraordinary feat of strength. There's one particular line that stands out:

Men gasped and began to breathe again, unaware that for a moment they had ceased to breathe.

The atmosphere's so tense that the men aren't even breathing properly. But as Buck gets nearer and nearer to the finish line, the cheering starts getting louder and louder. The crowd knows that this remarkable dog is going to succeed. Buck will make it, and he does.