We study the power control problem in wireless ad hoc networks with selfish users. Without incentive mechanisms, selfish users transmit at their maximum power levels at the Nash equilibrium (NE), causing significant interference to each other. In order to induce users to transmit at desired power levels, existing works have proposed pricing and auctions as incentive mechanisms. With pricing or auctions, it is explicitly stated or implicitly assumed that the users are obedient, in that they adopt the utility functions designed by the system and accept the prices as control signals. In this paper, we use the intervention mechanism to incentivize selfish users to achieve efficient outcomes as the (unique) NE. In the intervention mechanism, a system designer prescribes a intervention rule and uses a intervention device to execute it. Depending on the monitoring technology and intervention capability of the intervention device, we propose two types of intervention rules with different performance and complexity tradeoffs. We study the performance achievable by the proposed intervention rules, as well as the design principles for different intervention rules. We prove that all the Pareto boundary can be achieved as the NE or even the unique NE of the game with intervention. Simulation results demonstrate the performance improvement achieved when using different intervention rules and illustrate performance analysis on different intervention rules.