The authors describe a simple modification to the injection seeding method which has proved experimentally to yield reliable, single-mode emission from a 10-atm CO2 laser without the need for cavity length tuning. The technique consists of choosing the laser parameters such that the power oscillator is operated slightly below emission threshold, even though the gain can be above threshold for a short time following excitation. Under such circumstances, the initial laser power due to spontaneous emission is too weak to be amplified to a significant level during the period where the gain exceeds the losses. If a more intense external signal is injected into the laser, it can be regeneratively amplified to much higher powers, eventually extracting a substantial fraction of the available laser energy. Therefore, the laser emission is totally controlled by the external signal; parasitic multimode pulses are completely absent. A simple analysis is also presented that describes quantitatively the dynamics involved in the process.