Wozniacki remained undefeated advancing with a 7-5, 6-3 win over American teenager Christina McHale.
Three-time defending champ Wozniacki has a perfect 15-0 career record at the annual final tournament before the US Open, which begins in four days.
Wozniacki broke McHale's serve in the eighth game of the second set of the one hour, 42 minute centre court match.
China's Li endured several hours of rain delays before advancing with a 6-4, 3-6, 6-2 quarter-final victory over Russia's Anastasia Pavlyuchenkova.
Li will play Czech qualifier Petra Cetkovska who beat fourth-seed Marion Bartoli 7-5, 7-5.
Wozniacki will face third-seeded Francesca Schiavone, who advanced without hitting a shot after Anabel Medina Garrigues withdrew due to a knee injury.
Medina Garrigues, who was seeking a third title of 2011, fell to the ground and grabbed her knee after failing to convert a third match point in the second set of her 6-2, 7-6 (7/5) victory on Wednesday.
With the start of the US Open looming on Monday, Medina Garrigues said she didn't want to take a chance on making her knee worse.
She is the 30th seed for the final Grand Slam of the season and due to take on a qualifier in the opening round.
Even as they battled to get through the day's matches, officials of the Open tune-up moved up the start of the championship match on Saturday in hopes of beating Hurricane Irene.
The tournament is scheduled to end on Saturday to allow players time to prepare for the US Open.
Organizers moved the start time of the final four hours to 1:00 pm (17:00 GMT) on Saturday.
Hurricane Irene, packing winds of up to 185 kilometres (115 miles) per hour, has already brought destruction to the Caribbean and Bahamas as it roars toward the East Coast of the United States.
Irene is expected to slam into North Carolina on Saturday and eventually to reach the New York area, which usually only experiences the remnants of hurricanes.
New Haven organizers have already had to cope with Mother Nature this week.
On Tuesday, play was suspended for more than two hours as the earthquake with an epicentre in northern Virginia shook the stadium.
Tuesday's 5.8 magnitude quake was felt as far south as Alabama and as far north as Toronto. (AFP)
