We demonstrate a simple approach for broadening and compression of intense pulses at megahertz repetition rates by self-phase modulation in nonlinear photonic crystal fibers. In order to avoid damage by self-focusing, we positively chirp the input pulses, which allows coupling of significantly more energy into the fiber, while maintaining the same spectral bandwidth and compression as compared to the Fourier-limited case at lower energy. Using a commercial long-cavity Ti:sapphire oscillator with $55\mathrm{fs}$ , $400\mathrm{nJ}$ pulses at $5\mathrm{MHz}$ , we generate $16\mathrm{fs}$ , $350\mathrm{nJ}$ pulses, which is a factor of 4 more energy than possible with unchirped input pulses. Self-phase-modulated spectra supporting $11\mathrm{fs}$ duration are also shown with $350\mathrm{nJ}$ pulse energy. Excellent stability is recorded over at least $1\mathrm{h}$ .