Does a replacement effect that replaces drawing a card apply to the opening hand draw?

The opening hand is distributed during the pregame procedure, governed by CR 103.4. Each player simply 'receives' their starting hand of seven cards; this is explicitly distinct from the game action of drawing a card.

Drawing a card is a defined game action under CR 121.1: a player draws a card by putting the top card of their library into their hand. Replacement effects that modify drawing (e.g., 'If you would draw a card, you may instead...') only intercept that specific game action, not the pregame dealing of cards.

Because the opening hand is not a draw under the rules, effects like Teferi's Puzzle Box, Replacement Cerulean, or similar 'whenever you draw' or 'if you would draw' effects simply do not trigger or apply during that setup step. The same logic applies to effects that trigger 'whenever a player draws a card' — no draw occurred, so no trigger fires.

Concrete example: You have Narset, Parter of Veils on the battlefield, which limits opponents to drawing at most one card per turn and would otherwise replace additional draws. When your opponent receives their opening hand of seven cards, Narset's replacement effect does not interact with it at all — all seven cards are dealt normally.

The mulligan process (CR 103.4) involves looking at and potentially returning your hand and 'drawing' a new one via the London Mulligan, but even there, the rules treat the initial deal as setup, not a draw. Always check whether an effect specifically references 'the opening hand' to interact with that phase.