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Everything had to go right in the final period for the Portland Trail Blazers to win their Game 4 matchup with the Dallas Mavericks on Saturday.

And it did.

The Trail Blazers, led by guard Brandon Roy, embarked on an historic comeback, rallying from 23 points down in the second half, including an 18-point deficit in the fourth quarter to defeat the Mavericks, 84-82, to tie their best-of-seven series at two games apiece.

Roy was spectacular, scoring 24 points in 24 minutes, including 18 in the fourth quarter. His biggest shot came with 1:06 remaining and the Blazers trailing, 82-78, when he drilled a three-pointer from the left wing and was fouled. His free-throw tied it at 82, and, after Dallas missed a three-pointer on the other end, Roy finished off his masterpiece, banking in a 9-footer in the lane with 39.2 seconds left to give Portland its first lead since it was 9-8.

Roy scored the Blazers' final eight points.

It was the second-largest comeback in the fourth quarter in NBA playoff history. The largest came in 2002 when Boston rallied from a 21-point deficit in the fourth quarter of Game 3 of the Eastern Conference Finals to defeat New Jersey. Portland's comeback tied Phoenix, who rallied from an 18-point deficit in Game 2 of the 1994 Western Conference Semifinals in their overtime victory against Houston.

Portland went into the half trailing just 37-35, but Dallas began the third quarter on a 27-6 run to take a 64-41 lead with 2:49 left in the period.

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And that's when the Blazers began their final run.

With the Mavericks still maintaining home-court advantage, conventional wisdom would say that they're in the driver's seat. But Dallas, which has been eliminated in the first round of the playoffs in three of the last four seasons, twice as the higher seed, must exercise its postseason demons. In 2007, the Mavericks, after going 67-15 in the regular season, were defeated by No. 8 seed Golden State in the first round, and, last season, seventh-seed San Antonio ousted Dallas in six games, also in the first round.

So, the question remains: What will be the psychological hangover for Dallas come Game 5?

Whether history has any bearing on this matchup remains to be seen, but one thing's for sure: this is shaping up to be quite a series.