Dueling Banjos in First Quarters

Watching the first quarter of the Phoenix-Portland Game 5 on Monday night, I noticed a true tale of two cities: Portland smashed the Suns in the first six minutes, while Phoenix dominated the latter six. The Blazers jumped out to a 23-9 lead early, but Phoenix registered an 18-5 burst to bring the score back to 28-27 by the first intermission.

Anecdotally, I feel like I've seen many games where two teams exchange dueling first-quarter runs. We rarely see dueling third-quarter runs, for example. A lead in the third quarter is more likely to "stick" (focusing only within the third quarter, not on future developments) than a lead in the first quarter is likely to stick (focusing only within the first quarter, not on future developments). What's more, on a subjective emotional level, players and observers don't take a first-quarter lead very seriously.

Sadly, I do not have the data to evaluate whether my anecdotal impressions are spot on. Still, assuming I'm not entirely delusional, here are some explanations I can think of to explain this phenomenon.

1) Teams in the first quarter are physically fresher, so better able to execute a "run".
2) Teams in the first quarter haven't yet figured each other out defensively.
3) Related to (2), a team in the first quarter may actually encourage the opposing side to go all-out offensively, so that the defensive team can see what's in the offensive team's bag of tricks. Imagine the feeling-out process between two boxers.
4) Teams in the first quarter aren't trying as hard defensively, because they figure they have the whole game ahead of them to erase any deficit.
5) The home crowd may have more energy in the first quarter. (But this doesn't explain how the road team is able to execute a run in the first quarter.)

Which of these possibilities is the most salient?