The lectionary used in my parish church very clearly states in the ‘Ordinary Time’ section that ‘The first Sunday in Ordinary Time is the Baptism of the Lord.’
However, the readings for the Baptism come at the end of the section headed ‘Christmas.’
My ‘Daily Roman Missal’ has got ‘Baptism of the Lord’ listed at the beginning of the section ‘Ordinary Time’ (published by Midwest Theological Forum, USA, 2010, p. xxxvi), and not in the Christmas season.
We’re going round and round about this here in Poland (where we use that English-language lectionary from the US, published by USCCB, and where Epiphany is always on the 6th, no matter what day of the week, and is a holy day of obligation) because in this country, they extend the Christmas season right up until February 2, keeping all Christmas decorations up and singing Christmas carols at every Mass until the Presentation (or ad nauseum, which usually comes first). So even though they are announcing that it’s Ordinary Time and reading OT readings and using OT propers, they keep singing and decorating the church as though it’s Christmas - in some years until as few as 4 days before Ash Wednesday. The only explanation I get about this - from a bishop, a priest and an informed church organist - is that they really like Christmas carols and have a lot of them, so they keep singing them (and I guess that’s why they keep the decorations up: because they really like it. Go figure.).
Joe Kelly’s explanation makes the most sense to me. You can’t have a ‘second’ unless you have a ‘first,’ just as you can’t have a son unless you have a father. It doesn’t make sense to me - as someone proposed elsewhere - that the second Sunday in OT is really ‘the Sunday in the Second week of OT’ because it still leaves you without a Sunday in the first week of OT, and what kind of week has no Sunday in it?
It seems that logically it’s got to be the First Sunday in Ordinary Time which is trumped by the Baptism of the Lord.