The Liberty (16-18) needed a win to qualify for the play-offs after the Washington Mystics beat the Connecticut Sun 76-74 before New York took the court on Sunday.
With the pressure on, the Liberty rose to the occasion, qualifying for the play-offs for the first time since 2005.
Both the Mystics and the Liberty finished the season with the same record, but New York won three of the four match- ups during the regular season to hold the advantage in the head-to-head tie-breaker.
The Liberty will face the Detroit Shock on Friday in Game One of the best-of-three series.
The Shock, who are the reigning WNBA champions, finished with the league's best record at 24-10 but split the season series 2-2 against the Liberty.
The Sky (14-20) shot just 20% (eight of 40) from the field in the first half as the Liberty took a seven-point lead into the locker room.
Chicago responded by outscoring New York 24-10 in the third quarter to take a 45-38 lead into the fourth.
Strong low-post play by Cathrine Kraayveld, who had 12 points and nine rebounds, helped pull the Liberty back within one point before Shemeka Christon hit a three-pointer to put New York back on top with 5:58 left in the game.
The Liberty extended their lead to 53-50 with 1:42 left when Christon hit a fadeaway jumper before Kraayveld drove the lane and hit an underhanded lay-up to give the Liberty a five-point lead with just under a minute to play.
Christon, who finished with 15 points, iced the contest with a three-pointer with 23 seconds left.
Alana Beard scored 21 points and DeLisha Milton-Jones added 18 and seven rebounds as the Mystics used a stellar
third quarter en route to a 76-74 win over the Sun in the regular-season finale for both teams.
Nakia Sanford collected 14 points and 15 rebounds for the Mystics (16-18), who outscored the Sun 26-14 in the third period to take control of the game.
Washington went on a 14-0 run to start the quarter. Beard was nine of 17 from the field and added five rebounds and
five assists, while Milton-Jones shot eight of 24 from the floor.
Sanford was five of 11 from the field and collected five offensive rebounds.
All-Star Katie Douglas scored 21 points and Nykesha Sales added 17 for Connecticut (18-16), who shot just 42% (25 of 60) from the field, including eight of 22 from the arc.
The Indiana Fever finished the season on a positive note, but the same can't be said for the Detroit Shock.
Tamika Whitmore scored 18 points off the bench and Anna DeForge added 17 and eight rebounds as the Fever posted a 72-66 triumph over the Shock.
Despite not having All-Star Tamika Catchings in the line-up since late June, Indiana (21-13) ended the campaign winning four of six to prepare for a first-round match-up against third-seeded Connecticut (18-16).
Tammy Sutton-Brown's lay-up with 5:20 left snapped a 59-59 tie, sparking a 9-2 surge as the Fever grabbed the lead for good and never looked back.
With the Eastern Conference already wrapped up and home-court advantage throughout, Detroit (24-10) rested starters in the fourth quarter to extend their slide to four games.
Kara Braxton and Plenette Pierson each scored 13 points for the Shock, who will host the fourth-seeded New York Liberty (16-18) in the opening round of the play-offs next weekend.
The Minnesota Lynx salvaged the final game of their disappointing season, beating the play-off-bound San Antonio Silver Stars 81-55.
Kristen Mann scored 19 points and Noelle Quinn dished out 14 assists to lead the Lynx, who finished the season with a 10-24 record, tying the Los Angeles Sparks for last place in the Western Conference and the worst record in the
Minnesota outscored San Antonio 30-10 in the third quarter to take a 58-41 lead which they would not relinquish in the final quarter.
The Silver Stars were without the services of leading scorers Becky Hammon and Sophia Young, who were rested by coach Dan Hughes in preparation for the first-round match-up against the reigning Western Conference champion
Sacramento Monarchs (19-14).
Rookie Shanna Crosley took advantage of her first start of the season, scoring a game-high 20 points for the Silver
In a potential second-round play-off match-up, Diana Taurasi scored 24 points to lead the Phoenix Mercury to a 87-73 victory over the Sacramento Monarchs.
Penny Taylor added 14 points and was 10-10 from the foul line while Cappie Pondexter chipped in with 13 for Phoenix (23-11), who finished the season by winning their last five games and 11 of their last 12.
Holding a 43-40 advantage at the start of the third quarter, Phoenix, the top seed in the Western Conference, put the game away with a 17-5 run to take a 65-50 lead.
Taurasi and Taylor combined for 15 of the 17 points.
The Monarchs (19-15), who finished the season 5-6 in their last 11 games, hit only one field goal in nine attempts during that stretch.
With their first two points in the second quarter, the Mercury broke a WNBA scoring record for most points in a
season by a team.
It was the second consecutive season under coach Paul Westhead the Phoenix set the mark. Rebekkah Brunson scored 19 points and Yolanda Griffith added 11 for the Monarchs who are the third seed in the west.
Finally, Tina Thompson scored 22 points and grabbed seven rebounds as the Houston Comets defeated the Los Angeles Sparks 82-72.
Tamecka Dixon collected 12 points, seven rebounds and six assists as Houston
(13-21) finished fifth in the Western Conference, four games out of the final play-off spot.
Hamchetou Maiga-Ba had 15 points and Michelle Snow added 10 for the Comets, who shot 48% (31 of 64) from the field and closed out the game on an 8-0 run.
The Sparks were led by Sherill Baker, who scored 16 points and dished out seven assists.
Jessica Moore scored all of her career-high 13 points in the first half and added eight rebounds for Los Angeles (10-24), who committed 20 turnovers en route to finishing the campaign tied with the Minnesota Lynx for the league's worst record.
Sidney Spencer chipped in 11 points for the Sparks, who shot 44% (27 of 62).