Ashley Hodson put the Reds ahead in the Group One North opener at Prenton Park and Niamh Charles restored their lead after Katie Wilkinson levelled.
But Maddy Cusack rifled in a second equaliser with three minutes remaining.
Liverpool’s Jade Bailey was then sent off and Pennock won it in added time.
Cup holders Manchester City made a winning start to their campaign as they swept aside Leicester 5-0, with Caroline Weir and Pauline Bremer both netting doubles before Tessa Wullaert added the fifth with a curling strike.
Last season’s runners-up Arsenal matched that scoreline, with striker Beth Mead grabbing a hat-trick in her side’s rout of London City Lionesses, while Jill Roord and Emma Mitchell also found the net.
Brooke Chaplen scored a goal in each half as Reading eased to a 4-0 success at Tottenham, with Ashleigh Neville putting through her own net before Millie Farrow hit the fourth.
Molly Sharpe’s double helped Durham to a 3-0 win against Aston Villa, while Kayleigh Green netted two penalties in Brighton‘s 3-0 victory at Charlton and Rea Laudat hit the winner as Crystal Palace saw off Lewes 3-2.
Coventry United collected a bonus point by beating Blackburn 4-3 in a penalty shootout after the sides had fought out a 1-1 draw while Bristol City defeated London Bees 3-0 with goals from Carla Humphrey, Ebony Salmon and Abi Harrison.
BBC Sport has launched #ChangeTheGame to showcase female athletes in a way they never have been before. Through more live women’s sport available to watch across the BBC in 2019, complemented by our journalism, we are aiming to turn up the volume on women’s sport and alter perceptions. Find out more here.