Rio de Janeiro: The star Indian duo of Sania Mirza and Rohan Bopanna entered the semi-finals of the mixed doubles tennis event at the ongoing Rio Olympics by defeating Andy Murray and Heather Watson of Britain in straight sets here. The Indians won their quarter-final match 6-4, 6-4 in one hour and seven minutes at the Olympic Tennis Centre here on Friday. The fourth seeded Indian duo dominated their British opponents with both Sania and Bopanna coming with some fine work at the net and excellent returns of serve. Murray was clearly struggling with his fitness after having played a gruelling men's singles match earlier on Friday and both Sania and Bopanna admitted that containing him was the key to winning the match. "We saw Andy's match last night and our gameplan was to try and take him out of the game as much as possible and play to his weakness, if he has a weakness. It was also to take the ball as much as possible to Heather. Andy was serving and volleying and for me that's a good target," Sania said after the match. "The conditions today were favourable. It was not so windy even though Andy Murray was playing amazing tennis.. The only way to win the game was to keep Andy away from the ball. And Sania hit the ball very well and helped me move well too. I also served very well today. Luckily we got a clean match in straight sets," Bopanna said. "Andy missed a few first serves and we capitalised on it. There was a lot of pressure on Andy since he was covering three-fourths of the court. You can't say there were weak points with Heather. What we had to do was keep away from the strong man," he added. The Indian duo had a shaky start as Murray and Watson broke Sania's serve in the second game to take a 2-0 lead. But Sania and Bopanna replied in kind in the very next game to force a service break of their own. Sania then saved a break of serve in the third game before Bopanna held his serve with a powerful ace in the sixth game to level the scores at 3-3. The Indians broke Watson's serve in the next game to take a 4-3 lead, thanks to some excellent returns, including superb returns by Sania at the net. The Indians then brushed aside a strong fightback by the British duo in the next game as Sania held her serve. Murray held his serve to reduce Sania-Bopanna's lead to 5-4, but a couple of brilliant aces by Bopanna in the next game handed the opening set to the Indians. The second set went with the serve until the Indian pair broke Murray's serve to take a 3-2 lead. Up by 4-2, Sania and Bopanna stretched Watson's serve to 0-30 before the Britons managed to avert another service break. The Brits tried and staged a desperate fightback as both teams continued to hold their serve. But the Britons could not rejoice for long. Serving for the match at 5-4, Bopanna produced a couple of booming aces to clinch the game and send the sizeable Indian contingent among the crowd into celebration mode. Sania asserted that she was satisfied with her performance on Friday, adding that they will need another superb performance in the last four stage. "I was returning better today and Rohan is such a solid player. We win most of the time with his serves, unless I do something stupid. We had gameplan and we stuck to it. We played better than yesterday. My returns also worked very well and I was hitting fast and deep, and Andy had to help Heather there. Our gameplan worked well today," she said. "Yes we ran into each other on two occasions when he wanted to take my forehand really badly and at one point when I had to get out of the way and did not move out fast. The reaction time on the court is in milliseconds. “In a mixed doubles match the girl is going to get most of the balls. I know that as a girl I am going to be attacked no matter what happens. So it was with Heather. As a girl you have to expect that because the guys are serving better and hitting harder. Of course, if an opponent has a weakness, like a weak backhand, we will go there," she added. Sania, who is the World No.1 in women's doubles, asserted that the Indian duo still have a lot of work to do before they can be assured of a medal. "A win gives you a lot of boost, but every day is new day and we will come out and fight again tomorrow and give it our best. I and Rohan have a good chemistry and we have a lot of fun on the court and fight well together. It helps that we know each other off the court as well. Even in an intense situation we help each other very well," she said. "We played two champions today and we are going to play two champions tomorrow."