No time in any way affects the ability to get pregnant. Well, more precisely, there are indirect circumstances that may affect.
So, if you use contraception such as condoms, then here you practically take all the most adequate measures in order not to get pregnant.
Ovulation has the highest risk of pregnancy and you need to be as careful as possible. And so, the first time you have, the third in a row or the third in principle - there is no difference.
therefore my answer, in your example, you can not
The key question here depends on "protection". What kind of protection? If it was a condom that was worn from the very beginning of the act, then you can live in peace. And if there was simply an interrupted intercourse, then the likelihood of pregnancy is very high.