Earlier, Ukrainian Elina Svitolina prevailed in the longest tie-break of the season to beat Czech world No. 2 Karolina Pliskova 7-6 (14-12), 6-4 in their purple group round-robin clash.
Halep and Andreescu held their opening services in the first set and then traded breaks to go 2-all. Andreescu then turned up the heat, firing 15 winners against Halep's 5 on the way to breaking her twice more and stitch up the opening set.
Halep went a break up at 3-2 in the second set, but Andreescu reduced the arrears with exactly the kind of athleticism she is known to bring to the court, managing to find returns and stay in rallies that would confound other players.
During a medical timeout for Andreescu at 4-all in the second set, Halep called for fitness coach Darren Cahill, who encouraged her to keep her shots low and focus on improving her first service percentage.
This advice turned out to be exactly what Halep needed. Although Andreescu broke her to pull level at 4-all, Halep would go on to stave off a match point and force a tie-break with a spectacular backhand down the line that Andreescu was powerless to answer.
The two players traded crosscourt backhands throughout the tie-break, but it was Halep who proved able to crack her opponent and force a decider with a mix of passing shots and lobs that kept Andreescu off balance.
Although it was Andreescu who broke first in the third set, Halep answered immediately with a break of her own and it was clear that she had found the form that had alluded her early in the match.
She went a break up at 5-3 and went on to serve out the set with a hold to love that delighted the very pro-Halep crowd on court at the Shenzhen Bay Sports Center.
Halep called Andreescu a tough opponent in the on-court interview after the contest.
"It was a very tough match. I knew that she's a very great player and that she's in it until the end," Halep admitted.
( With inputs from IANS )