The Heat and Celtics get back at in Thursday night at 8:30 p.m. ET.
The Heat and Celtics get back at in Thursday night at 8:30 p.m. ET. IBTimes Pictures

A trip to the NBA Finals will be on the line when the Boston Celtics host the Miami Heat at TD Garden in Game Six of the Eastern Conference Finals on Thursday night.

After dropping the first two games of the series, Boston defeated Miami in the next three games to take the series lead. Many experts were surprised by the aggressive play of the veteran Celtics, as the Heat were considered the more athletic and hungry squad.

But Miami will likely be at their best in Game Six, as the most contentious team in the NBA tries to avoid an upset.

Here are five keys to watch for in Game Six.

Which Rajon Rondo will show up? Rondo is arguably playing the best basketball of his career. The Celtics point guard has posted three triple-doubles this postseason, and two assists short of his fourth in game two against Miami. In that game Rondo torched the Heat for a career-high 44 points. If the Heat cannot prevent Rondo from penetrating into the paint and making jumpers from the free throw line, Boston has a good chance of advancing to the NBA Finals.

LeBron James in the fourth quarter James has been the focus of much discussion during the 2012 NBA Playoffs. The superstar small forward has been particularly effective on both ends of the court, and has led the Heat in scoring with an impressive 29.9 points-per-game average. The big question is whether James can prove his critics wrong and step up in the fourth quarter, does he posess that killer instinct to close out games? If he can dominate the fourth quarter the Heat stand a good chance of forcing a Game Seven in Miami.

The Presence of Chris Bosh The Heat big man may dictate the flow of the Game Six. Bosh suffered an abdominal injury during Game One against the Pacers in the Eastern Conference Semi-Finals, and missed the rest of that series and most of the Conference Finals. Bosh's return in Game Five was a major storyline, but he only played 14 minutes. Bosh is set to start in Game Six and Heat head coach Erik Spoelstra expects him to play a much bigger role. A healthy Bosh should disrupt the scoring of Celtic forwards Kevin Garnett and Brandon Bass, two players who are imperative to the Celtics offense.

Is Paul Pierce The Truth? Game Five may have been Pierce's most clutch playoff performance of his illustrious career. The veteran forward buried the dagger in the Heat in the fourth quarter when he knocked down a jump shot in James's face. It seemed as if Pierce was giving James a lesson in closing out games in the clutch. The Truth finished Game Five with 34 points and has been a force to reckon with the entire series. It is almost certain that James will guard Pierce tonight, especially in the fourth quarter. Pierce's experience and perimeter skills should have a major factor on the outcome of Game Six.

Officiating The referees have been criticized for most of the series. In Game Six, the crew should probably swallow their whistles when it comes to off-the-ball fouls, as well as technical fouls. The referees called the first two games very tightly, which played heavily in the Heat's favor. Celtics head coach Doc Rivers and Garnett were both given questionable technical fouls early in the series. In the last three games, the officials have relaxed a bit with their whistles and held back on petty fouls. Emotions will being extremely high for the rest of the series, so it will be interesting to see if the officials call the game loose or tight.