This idiom or expression like phrase (in sports) means:

Not enough challenge.

When someone says “Did you see the match last night? It was no contest,” they mean:
It wasn’t a fair match.
The two sides were not fairly matched.
One side was very clearly superior to the other. Etc.

This idiom or expression can best be explained as follows:

When one side is clearly and overwhelmingly superior to the other side, a comparison or competition between the two sides becomes meaningless and won’t be fair. In such cases, the less superior side is no match for the other one.

Examples:
A slide rule is no match for modern calculators.
A car is no match for a truck, if we’re talking about load capacity.
A bicycle is no match for a motorcycle, if we’re talking about speed. Etc.