Keothavong stuns Ivanovic in Luxembourg
Keothavong, who had to come through three qualifying matches just to make the main draw, took full advantage of an off-colour performance from Ivanovic to record an impressively easy 6-3 6-2 win.
Ivanovic was particularly abysmal on second serve, winning just three points out of 23 when she failed to get her first serve in, and as a result she was broken six times during the match.
Another sub-plot to the win is the fact that Ivanovic is coached by former LTA women's head coach Nigel Sears.
Keothavong, who has been ranked in the world's top 50, is currently ranked 96th in the world, but could be in line for a big jump this week.
She is now in the quarter-finals and in a half of the draw that contains no remaining seeds.
She will face Bibiane Schoofs of the Netherlands in the last eight after Schoofs beat Canada's Rebecca Marino 1-6 6-1 7-5.
The winner of that match will then take on Lucie Hradecka or Monica Niculescu for a place in the final.
Anastasija Sevastova of Latvia booked a last eight date with sixth seed Julia Goerges after a 6-2 6-2 win over Romania's Simona Halep.