Playing gomokunarabe on an international server, I saw a couple of Russian players saying "выиграть его," and the intended meaning apparently was "to win against him" as far as could judge from the context.
I got puzzled, because I had been taught that the correct way to say "to win against him" is "выиграть у него."
I did some research in Google and found that the preposition "у" is indeed frequently omitted:
(1) Впервые ХК «Сахалин» выиграл соперника всухую. (Source)
(2) Мирза Абдуллабеков боролся в категории 66 кг, представлял Республику Беларусь. В 1/8 финала выиграл соперника из Италии, в ¼ выиграл американца, в ½ встретился с французом, которому проиграл. За бронзовую медаль выиграл борца из Польши. (Source)
(3) В финале весовой категории 75 кг осетинский борец выиграл соперника из США Брэдли Гиллума со счетом 11:0. (Source)
(4) Я выиграл соперника в честном бою один на один, а не 30 на одного, когда они напали на автобус. (Source)
It is obvious that these examples are not typos. These sentences are from various sport articles, and Sentence (1) is even an article title. Sentence (4) is from the central Russian sport newspaper Sport Express. I also found really many similar examples.
I asked one of my teachers about this, and he said that "выиграть кого-то" means "to win someone as a prize." He insisted that the only grammatical way to say "to win against someone" is "выиграть у кого-то." But I did not show him any examples from sport articles, because I did not want to make him feel that I doubt the validity of his words.
I also found the following example in Google:
(5) Ты выиграл женщину, а я ничего. Чего тебе еще надо? (Source)
Apparently, this sentence is about winning a woman as a prize, not about winning against a woman.
I am so much confused. It looks like either many Russian journalists do not speak their own language properly or I was taught wrongly.
My question is this: Is it correct to say "выиграть соперника" if the intended meaning is "to win against the opponent"?
If yes, I want a reference to some reputable grammar source that explicitly allows omitting the preposition у in such phrases.
If no, I would like to know how it is that so many Russian journalists use that phrase.