Step 1: Historical context.
Chimajiappa, the brother of Bajirao Peshwa I, led the Marathas in the battle of Vasai against the Portuguese in 1739. He successfully defeated the Portuguese and secured Maratha control over the region.
Step 2: Conclusion.
The correct answer is Portuguese, as Chimajiappa defeated them at Vasai.
Final Answer:
\[
\boxed{ \; Portuguese}
\]