Top seed Simona Halep was pooled with Grand Slam winners Maria Sharapova and Flavia Pennetta in a formidable looking Red Group for the end-of-season WTA Finals on Friday. With world No 1 and defending champion Serena Williams opting out after narrowly missing out on a rare calendar Grand Slam, Romanian Halep is the highest seed for the eight woman end-of-season championships which begins on Sunday. Halep, who lost to Williams in the final last year after beating the American in the pool stage, was drawn against Italian Pennetta, who lifted a shock US Open title after compatriot Roberta Vinci beat Williams in the last four.