Ionescu made a franchise-record and career-high eight 3-pointers, the last putting the Liberty at the 100-point mark for the first time this season. She made 10 of 18 shots from the field, including 8 of 13 3-pointers and added 9-of-10 from the free throw line.
Ionescu said she didn't know at the time that she was on the precipice of franchise history.
"I didn't know what the franchise record for 3s was. But they were going under (the screen) -- as a shooter that's the most disrespectful thing you can do, so I shot it when I was open," Ionescu said after the game. "My teammates got me the ball and great actions. I was just thankful we won at the end of the day. I was just making the reads and shooting if I'm open."
Atlanta trailed 61-39 at halftime but closed to within 67-60 late in the third quarter. A steal and fast break layup by Marine Johannes put the Liberty up by nine, and New York finished the quarter on a 10-0 run. The Liberty added six points to their lead in the fourth quarter.
Atlanta led 15-13 in the first quarter before Stewart went on a nine-point scoring spree that included two 3-pointers, one of which became a four-point play. The Liberty led 26-19 at the end of the period.
Haley Jones hit a 3-pointer, got a rebound at the other end and hit a short jumper to draw Atlanta into a 33-all tie midway through the second quarter. But the Dream never took the lead and New York responded with a 14-1 run in which Ionescu scored 10 points. Her 20 points in the quarter were two shy of the WNBA record. She had 23 points in the first half and New York led 61-39 at the break.
The game was part of the Commissioner's Cup, in which New York is 4-2 and Atlanta's record is 1-2.
The Liberty bounced back after an 86-82 loss to Chicago last time out and their scheduled game against Minnesota on Tuesday was postponed because of poor air quality in New York.
The Associated Press contributed to this report.