Championship tournaments for computer chess engines moved from onsite competition to online well before many human tournaments made the move last year in response to the COVID-19 pandemic. In recent years the Top Engine Chess Competition, which has been played virtually since 2010, has become the unofficial world computer chess championship.

In recent years, many of these competitions have been won by the open-source chess engine Stockfish, thanks to its ability to conduct deep searches of chess positions enabled by powerful computing. However, in 2019 the Stockfish engine was upended by the LCZero engine, which was developed using a very different approach, employing techniques that develop artificial intelligence. LCZero was launched in 2018 with no chess-specific knowledge other than the basic rules; it “learned” how to play by analyzing the results of millions of games played by volunteer users. This approach was extremely successful and led to LCZero defeating Stockfish to win TCEC tournaments in 2019 and 2020.

The Stockfish team responded by following the maxim “if you can’t beat ‘em, join ‘em.” In late 2020, a new version of Stockfish was introduced that complemented its deep position searches with a learning function similar to that employed by LCZero. The improved Stockfish has regained its top position among chess engines. In the latest TCEC championship, Stockfish trounced LCZero, with 19 wins and only seven losses in their 100-game match. Other chess engine developers have taken note, and all of the top-rated chess engines now combine classical computing with learning functions.

In the recent match, Stockfish often outperformed LCZero in games that reached unusual positions where deep position searches proved to be more valuable than evaluations that relied on prior learning. In Game 68, the following position was reached after lengthy maneuvering by both sides. LCZero evaluated the position as even, but Stockfish found an opportunity to unbalance the game, to its advantage, by offering a surprising bishop sacrifice.

White to Move

                                                  (Stockfish-LCZero Game 68 Move 180)

180Bf6! If black plays 180…gxh6? white has 181Rxh6+ Nxh6 182Rxh6+ Kg8 183Qh5 and white forces checkmate in a few moves. After further maneuvering, Stockfish intensified its attack on the black king by offering to sacrifice a second piece – its queen.

White to Move

                                                  (Stockfish-LCZero Game 68 Move 191)

191Qg5! The queen cannot be taken; 191..hxg5 192Rh8 is checkmate. Black has no satisfactory response. The game continued 191…Re8 192Rxh6! Nxh6 193Rxh6 gxh6 194Qxh6 when black must sacrifice its queen to delay checkmate.

Black to Move

(Stockfish-LCZero Game 68 Move 194)

194…Qg7 195Bxg7 Rxg7 196f5 exf5 197Qg5. Black can’t capture white’s e-pawn; 197…Rxe5? 198Qd8+ and white is about to checkmate.

197…Rf8 198e6 Rc7 Stockfish now maneuvers its King to g5, freeing up the queen to harass the black king and rooks.

199Kc3 Rg7 200Kd4 Rc7 201Ke5 Rg7 202Kf4 Rc7 203 Qh4 Rg7 204Kg5 Re7 205Qf4 Kg7 206Qd6 Rfe8 207Qe5+ Kg8 208Qf6 LCZero is reduced to pawn moves, because moving its king or either rook leads to immediate disaster. The game continued until checkmate, per TCEC tournament rules.

208…b6 209axb6 a5 210Qf7+ Rxf7 211gxf7+ Kf8 212fxe8+ Kxe8 213b7 Kf8 214Kf6 Kg8 215b8(Q)+ Kh7 217Qc7+ Kg8 218Qg8 checkmate.

(Stockfish-LCZero Final Position)

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Keith Holzmueller has been the head coach of the Evanston Township High School Chess Club and Team since 2017. He became a serious chess player during his high school years. As an adult player, he obtained a US Chess Federation Expert rating for over-the-board play and was awarded the Senior International Master title by the International Correspondence Chess Federation. Keith now puts most of his chess energy into helping young chess players in Evanston learn to enjoy chess and improve their play. Please email Keith at if you have any chess questions.

Keith Holzmueller

Keith Holzmueller has been the head coach of the Evanston Township High School Chess Club and Team since 2017. He became a serious chess player during his high school years. As an adult player, he obtained...