What's the right word to describe a situation in a sports competition or in elections, in which both competitors are equal on all parameters and it is absolutely not clear which one of them will be the winner?
Not a single word, but the usual term is "wide open". See Collins Cobuild:
If you say that a competition, race, or election is wide open, you mean that anyone could win it, because there is no competitor who seems to be much better than the others. The competition has been thrown wide open by the absence of the world champion.
As JeremyC mentions, there is no single word for this, but there are multiple expressions. He already mentions "wide open", but there are others:
It's anyone's game.
It's too close to call (there is no way to confidently predict the winner).
It's a toss up (random, like tossing a coin)
It's a dead heat (as in a race, when neither runner is clearly ahead)
It's an even match/contest (neither participant has a clear advantage)
It's down to the wire (as in horse racing, with a wire across the finish line, and none of the horses clearly in the lead)
It's neck and neck (another horse racing expression, when the horses are too close together to see which is clearly in the lead)
Finally, there's the expression "photo finish", which is used after the race is over, but there is still no clear winner. Again, with horse racing, a photo would be taken at the finish line, then developed and examined to see which horse (if any) was ahead.
Naturally this can be used for any competition:
You might call it "close":
1.4 (with reference to a competitive situation) involving only a small margin between winner and loser.
‘the race will be a close contest’
‘she finished a close second’
You can also comment that it's "too close to call":
too close to call
COMMON If a contest is too close to call, it is impossible to say who will win, because the opponents seem equally good or equally popular. The presidential race is too close to call. Exit polls in Britain say that today's parliamentary election was too close to call.
Since you are looking for a single word, I would suggest crapshoot.
From the Grammarist, a crapshoot is a situation whose outcome is not predictable.
Of the five examples of usage at Grammarist, one refers to sports and another to elections:
Everybody knows that an election with a small turnout can be a crapshoot.
Talladega is a crap shoot, so you never know what’s going to happen.
Notice in the second example above, it is spelled as two words, which is less common.