Measurement errors make power analysis attacks difficult to mount when only a single power trace is available: the statistical methods that make DPA attacks so successful are not applicable since they require many (typically thousands) of traces. Recently it was suggested by  to use algebraic methods for the single-trace scenario, converting the key recovery problem into a Boolean satisfiability (SAT) problem, then using a SAT solver. However, this approach is extremely sensitive to noise (allowing an error rate of well under 1% at most), and the question of its practicality remained open. In this work we show how a single-trace side-channel analysis problem can be transformed into a pseudo-Boolean optimization (PBOPT) problem, which takes errors into consideration. The PBOPT instance can then be solved using a suitable optimization problem solver. The PBOPT syntax provides for a more expressive input specification which allows a very natural representation of measurement errors. Most importantly, we show that using our approach we are able to mount successful and efficient single-trace attacks even in the presence of realistic error rates of 10%-20%. We call our new attack methodology Tolerant Algebraic Side-Channel Analysis (TASCA). We show practical attacks on two real ciphers: Keeloq and AES.