Venus Williams a serious threat to Serena's calendar Grand Slam bid
![Venus Williams a serious threat to Serena's calendar Grand Slam bid](http://www.timeslive.co.za/Feeds/Reuters_Images/2015/09/08/2015-07-06t124940z_01_wim179_rtridsp_3_tennis-wimbledon-06-07-2015-17-07-33-206.jpg/ALTERNATES/crop_80x80/2015-07-06T124940Z_01_WIM179_RTRIDSP_3_TENNIS-WIMBLEDON-06-07-2015-17-07-33-206.jpg)
Serena Williams's historic bid to complete a calendar Grand Slam faces its biggest emotional test on Tuesday when she tackles sister Venus for a place in the US Open semi-finals.
Serena Williams's historic bid to complete a calendar Grand Slam faces its biggest emotional test on Tuesday when she tackles sister Venus for a place in the US Open semi-finals.