During the Last Supper, when Jesus told his disciples to drink the wine because it was his blood. Which cup of wine was this? Was it the third cup, or was it the cup of Elijah (or one of the other cups)?
(emphasis added, obviously)
This seems to indicate that it was the third cup.
Here is a much larger article about it.
This is presuming that it was the Passover meal at all.
What is important is the, binding tie, between the first Passover & Last Supper. God told Moses to take an unblemished 1 year old lamb & use it's blood to mark the door sides & top with same. This lamb must be roasted completely & consumed that night with bitter herbs & bread without yeast. God will pass over the houses so marked. He will take the first born of the unmarked houses,man or animal. So the lamb's blood saved us from bondage in Egypt. During the Last Supper Jesus took the cup of new wine, ie. the fruit of the vine, and said, " this is my blood " & the bread without yeast, " this is my body ". So the Blood Of The Lamb saved us ie., if Born-Again, for eternal life with the Lord. So you see that when Born-Again both Jew & Christian are connected to the Vine ( Jesus -the Son of God ) & are chosen to be God's Children.