Hi!
You can say both.
"Υπάρχουν τρεις ποδοσφαιρικοί αγώνες σήμερα"
or
"Έχει τρεις ποδοσφαιρικούς αγώνες σήμερα"
The second structure, that is idiomatic, is more common.
The verb "έχει" is followed by Accusative Case (ποδοσφαιρικούς αγώνες), whereas "υπάρχουν" is followed by Nominative (ποδοσφαιρικοί αγώνες).
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.