It's uncommon for the lower seed, who took games one and two, to become the home underdog in game three. In such scenarios, the home team has struggled, with a 1-4 straight up record and a 2-3 performance against the spread. This historical trend indicates that the Celtics, as the road fave, to have a strong chance of covering the first quarter spread.
Interestingly, this same situation and matchup happened in the 2019 Eastern Conference Finals, where the Celtics secured a nine-point lead in the first quarter against the Heat. This demonstrates their ability to come out with a sense of urgency and establish an early advantage.
More support for the Celtics' case is the statistical analysis since 2019. The Heat, when playing as home underdogs following a win in the playoffs, have shown a first-quarter margin of -7.2. Conversely, the Celtics, as road favorites following a playoff loss, is an impressive first-quarter margin of +7.8. These numbers suggest that the Celtics are primed to take control from the opening tip.
In conclusion, all signs point to the Celtics covering the first quarter spread. Their historical performance in similar scenarios, combined with the statistical advantages they possess, highlight their potential for a strong start.